Can you afford to pay the guy money? I would have a hard time giving up ownership in my company to someone who is just going to "do some development work". I think treating him as a contractor would be a good way to go from a business point of view, that way there is more flexibility for him to work his own hours and for you to avoid paying benefits, taxes, etc.
Giving some partial ownership in the profits of your individual project that he is working on may be a good way to benefit you both, but if he doesn't have a job do you think he'd want to wait that long before he finally got a check?
Unless of course, you want to make him a full blown part of the company, but it sounds like he just needs some temporary coding work for a short time and you guys could just use some help.
I think it is admirable that you are looking to take care of your friend and I think a flat hourly rate is probably best in this situation. It could be win/win for the both of you.
just my $0.02, I don't own a company.