Sorry. My first answer mis-understoood the question. Based on the updated question, there are many ways to create a shape of the desired profile, based on what tools you have or can find/buy/etc.
- Rip the edges with an angled tablesaw blade.
- A handheld power (circular) saw, with the blade at an angle. A fence will help you get a straight edge.
- A jointer.
- A handheld power jointer.
- A hand plane. A good craftsman with a sharp jointer plane can do this easily.
- A router table.
- A handheld router.
- A millwork shop can easily turn this profile out, so you can always buy it ready made, for a price.
- If you have a friend with any of the above power tools, I'll bet they can be bought off for the price of a pizza.
Very much depends on what tools you have, how much money you want to spend. You can use it to justify buying a specific tool, if you have a use for one of the tools I've mentioned. They are all useful.
A tablesaw or a router are both terribly useful tools, but if this is a one time job and you have no interest in woodworking, then I'd look for a friend who can help you out. If you insist on doing it yourself, and might have an occasional use for a hand held circular saw, then go that route. A circular saw will be often enough of use even to someone who is not an avid woodworker.
Attach your board to a straight piece of wood to use as a fence. Then angle the blade, and rip the edge as you want it. I'll argue this is the cheapest solution that will give you a good edge. (A hand held jointer plane might be even cheaper, since you can get them quite inexpensively from an antique shop. But a jointer plane will take some practice to do this job well.)
Wood can be plasticized by various methods ...
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_19.pdf
"Wood members can be readily molded or shaped after immersion in liquid ammonia or treatment under pressure with ammonia in the gas phase. As the ammonia evaporates, the lignin resets, the wood stiffens and retains its new shape. Plasticization of the lignin matrix alone can be done using chemical modification technologies, which are covered later in this chapter."
http://www.google.com/search?q=wood+plasticizing+wood
However, in this video interview of Gustav Reyes published about a year ago, he states (at 1:50 min) that he makes his wood jewelry using steam and compression.
http://www.youtube.com/watch?v=oq-zsyL3vZ8
However, he goes on to claim that the process was created 10-15 years ago.
Bending any wood, steamed wood included, puts compression on the fibers along the inner radius, and tension on the fibers along the outer radius. The tension acts to splinter the outer fibers. The compression acts to buckle the inner fibers. The solution, long known, is to apply a metal compression band while the wood is still straight before bending. The strap is placed on the surface that will form the outer radius. The strap greatly reduces the tension (splintering) of the fibers on the outer radius, which is good. But in doing so, it also increases the compression on the fibers along the inner radius, which can be problematic.
If the technique he uses is indeed 10-15 years old, then it is not mere steam+compression and he's told only part of the story. Plasticizing, as detail in the above PDF, is also and old technique, as is PEG impregnation. So the jury is out.
Best Answer
Use a router with a plunge base and either an edge guide or straight edge, depending on the size of your work piece. Attach stop blocks to the workpiece and/or straight edge (clamps would be one easy way to hold the stop blocks in place). The stop blocks will prevent you from cutting your slot too long. First set up the edge guide or straight edge with the appropriate offset for your router base, parallel to where you want the slot. With the router unplugged and the bit almost touching the wood, position the router bit where you want the slot to start. Then use the router base to gauge exactly where to position the stop and clamp it in place. Do the same for the other end of the slot, then proceed with plugging in the router and cutting the slot in several passes, going slightly deeper each time.
You can also use a router table to do something similar, but the steps for setup will be different since you won't be able to see the cut as you're making it. However, you will be able to use your router table's fence and possibly other T-track or miter track accessories.
Although your material isn't very thick, it's still not a bad idea to cut the groove in multiple passes.
In a pinch, you can also use a Dremel/rotary tool (which is essentially just a tiny, low-torque router) along with a router attachment and multipurpose spiral bit, but a router will give you slightly better results.
If you don't have a router, it's relatively easy to cut this slot by drilling a series of overlapping holes with a drill press and Forstner or brad-point bits, then clean it up with chisels.
No matter what solution you use, be sure to put a sacrificial piece of scrap wood on the back side of the workpiece to help prevent blowout when you cut all the way through to the other side.