hobby craft do self adhesive neoprene type sheets for about 80p for a4... it may not do exactly what you want but you'll be able to experiment by layering up strips... i used it on my springer to fill out the palm swell... it survived wales, and lithuania, and i don't think any fell off.
NSRA shop do something similar with an apparently almost indestructible glue for about 10x more. I bought some of that just in case. It's still in the shed.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep