Cooking ribs weirdly

My local lamb (grass paddock raised) just doesn't have enough fat on it to survive a "rack in the oven" experience. Hogget & mutton is fine. This may be your problem too?

So for lamb I would cleave the rack into individual ribs and BBQ on medium-high till the surface has crisped (typically twice as long as a similar beef cut). All the fat should have run. Most people I know don't like eating visible lamb fat

I lightly coat the cut meat surface with oil just before placing on BBQ to ensure an instant sear. You want the lamb to crisp without drying out

If using a wood fired BBQ drop a bunch of fresh lavender (leaf and flowers) under the grill to slightly smoke the lamb

You need high, direct heat.

Option 1 (The practical): Don't think about the candles. Even if you lit enough candles in a pile to get it hot enough- candle soot tastes terrible. Of all the tools listed among your assets only the grill shows potential. Buy some charcoal for it, get it rocket hot, and sear your ribs to perfection.

The charcoal will also add a little flavor. Not much since they won't be there long but more than a torch would.

Option 2 (The MacGyver as requested): Use your paper to make a large (3-5' diameter) paper-mache parabolic dish. Line the inside of the dish with your foil with the shiny side out. Experiment with a sheet of paper to find the focal point of your dish. Move the paper toward the dish until the focused light is a couple inches across. Take your dish outside in the sun and wave your ribs in front of it. Solar blow torch.