By way of example - it may or may not be the most accessible and appropriate, the fellow on this thread
used the plastic bands that people put on birds (legs) to identify them.
He had a problem using one that had a bit of moulding "flash" projecting from it, but having sorted that out, seems to have been successful.
Other than that of course, I have to point out the same as Jim - the pressure exerted by the flaccid glans/ shaft in terms of stretching, is pretty much negligible and would have a very
slow effect. The only
times it would really be of benefit - would in fact be those when you did
get an erection.
On the other hand, we suspect that even a few minutes a day of firm pressure (with the two fingers) is better than nothing.