A loose BB due to the BB shell being ovalized isn't something you can tighten with an allen wrench. Which part are you tightening with the allen wrench to make it useable for a bit longer each time? I suspect that we're all talking about different things here. The only thing that an allen wrench would be used for would be a wobbly crank arm mounted on a square taper or spline BB.

Can you give us a picture of what you have now and draw a nice colored arrow on the part that keeps coming loose that you're tightening? Because as it sits now the only thing I see in this thread is confusion.