Minecraft – way to keep Zombie Pigmen off of minecart tracks in the Nether

I am building a 2×3 tunnel for rapid travel (via minecart) through the Nether. The tunnel, in cross-section, looks like this:

 NN     N = Glass
N  N    X = Cobblestone
N_iN    i = Torch (alternating Redstone and regular torches, spaced out a bit)
NXXN    _ = Minecart track (alternating powered/unpowered)

I have read this question and the prevailing answer there basically says not to mind the Zombie Pigmen. For me, that isn't an option because Pigmen can be a bit of a showstopper to minecarts in my tunnel.

They spawn in the tunnel, as opposed to walking into it (this seems to be consistent with the Wiki article on Zombie Pigmen, which merely says they can spawn at "any light level". They're a problem because they appear in groups of 2-3 and prevent minecarts from moving along the track.

I have thought of a few possible ways to deal with this:

• Get off, pick up the minecart and walk around them, then put the cart back down and resume traveling. This is not ideal because I like to go AFK while on minecart tracks, and coming back to find I only traveled 50 meters before hitting a Pigman is frustrating.

• Punch a hole in the glass and shove them out into the lava. Again, this involves getting off the cart, and punching a hole in the glass makes the tunnel temporarily vulnerable to Ghast fireballs (thereby defeating the purpose of fully enclosing the tunnel in the first place).

• Attack them and move on. Not ideal because there is a good chance I will run into another gang of Pigmen further down the tunnel that will stop my cart and kill me while I'm AFK.

• Make the tunnel slightly taller, and make a trench on one side (or possibly both) into which the Pigmen can fall but from which they can't jump back up onto the minecart track. I'm not sure how effective this would be, as I'm not sure they would voluntarily wander into the trench.

There's also this design, found in a Minecraft Forums thread:

N    N = Glass
_    _ = Track
X    X = Cobblestone

Nobody can spawn (or walk) on your track, and the glass also keeps you from attracting ghasts. It's very relaxing riding across the netherscape in the apparent open, watching ghasts fly about overhead unaware of your presence.

I haven't yet tested it, but I would hesitate to embrace this design, as it seems like it's an exploit that is liable to be "fixed" in any given future update. (I just re-did about 4 km of track that was previously powered by exploiting the minecart collision bug/feature, and I do not want to go through that kind of thing again.)

Is there any non-exploit, modless way to keep my tracks clear of Pigmen? I should add that this is in the context of SMP, and I don't want to turn spawn-monsters off either.