Try some practice but on the real thing rather than a banana, use the real thing. My last bf had massive foreskin, what worked is to pull the foreskin all the way back, and unroll the condom all the way as far as it will go, then pull the foreskin foreword as far as it goes and finish unrolling the condom to the base. This works good as it allows the foreskin to move more as it naturally would and seemed to relieve the issue with being too sensitive. if the condom is not long enough to cover all the skin to the base as it didn't with him, simply pick out a bigger size ( Magnum; MagnumXL; Magnum XL10+ ). I hope this helps your problem.
2. Give your girlfriend the condom and let her unroll it onto you.