Smear peanut butter on the bread, NOW tear up the bread, and apply the peanut-butter-smeared shreds to the (peeled) banana.

Still the same primary advantage as pliny's method, same primary drawback (may not exhaust the bread), but we've solved the structure problem that you raise.

I feel the trend-line here is looking good; with a few more iterations, we may reach the true ideal PB&B sandwich.