Why not use cigalikes? Instead of them having to worry about dead batteries and refilling tanks, the shop could donate a percent of sales to purchase disposable no-name cigalikes for them at wholesaler cost. They're crazy cheap at wholesaler. Plus have a donation jar from customers. If my local B&M had one, I'd drop my change on every visit.
Much easier on both ends and sustainable. The homeless are issued two to three cigalikes - their choice of regular or menthol, and turn them in when dead to receive more. Swaps could be regulated to a certain time of day in order to make it easier. Maybe branch out to a few fruit flavors once the program gets rolling. They could even have a referral system with the local shelter handing out coupons to the people staying there to be able to get in this program, to weed out the freebie hunters. That ensures they only get people who actually want to quit, and helps control the flow so they don't get overwhelmed. (Can only support five people? Only print and issue five coupons.)
With disposable cigalikes, that also helps kill what everyone seems to be thinking will happen. They're really not worth a lot, and with a referral system, you know exactly who is who and who never turned in swaps, so they don't get more. Plus with swaps only at, say, 2-3 pm or whatever, they're not inconveniencing that many regular customers.
Many people don't give homeless a chance. A few bad apples made the whole bushel look bad. Why not take the time to check each one? There might be a few that surprise you.