been there, done that. i tried ww paint and those f*... loose whitewalls (portawalls) on my car, and neither is going anywhere near my bike. both are horrible.
but i found this company that can vulcanize (or whatever it's called) actual whitewalls on any car tire the same way that real whitewalls are made, as far as i understood anyway. i have just emailed them to find out if they can do the same with a motorcycle tire, i sure hope so.