You are up against a few things …
Managing a restaurant is a hectic job – I’m not surprised they don’t want to give any time to someone whose product does not improve their bottom line or service.
 
Unrequested solicitations (of customers) … while not quite panhandling … is still an unrequested solicitation to get money out of someone.
 
You’d be better off coming up with an advertising or PR campaign that will drive patrons to the restaurant, is quantifiable, and is at no upfront cost to the restaurant.  Then, you get a cut from each patron who indicates your program was a factor in their eating there.