It seems *very* risky to have any talk about any plans for BM to be involved, let alone fantasies about him mentioning this on Letterman.  Have you ever heard any celebrity endorsing products on Letterman?? Any celebrity endorsing an altcoin?  They are very risk adverse, with hucksters approaching them every day. They are turned off by it, like with Takeicoin and many other examples.

A low key key fan- and charity based approach is the best bet.  Keep the Twitter humming along supporting his charity. If it raises enough money for the Charity and finally gets through to him he may mention it or make a joke about it.   If you can eventually get a reasonable payment provider on board, you might ultimately get them to have it as a payment option.  This should be the blue sky goal, not endorsement on Letterman!