Tony, I do lots of production and recording on commercial music.
Part of the work is per hour or project. That would be for someone I don't know, who has no shot at volume sales.
Part is an hourly rate for the work, plus points. For example, 10 points is a dime a unit to me.
About 1/2 of the work is points only, because I only played on one or two cuts.
Still, some of the participation checks are healthy.
Sounds like you are a good friend, so if it were me, I'd negotiate a points mechanism if there is any chance there would be resulting sales.
Sadly, that's probably not going to happen in a major way, because of the business related issues a break-out writer/artist has to overcome.
Email me privately, and I can tell you what I know and connect you with people in the industry who do this all the time.
The original members of Exile are all friends and are involved in nearly every aspect of music production (think huge writing and production fees) in Nashville.
I have regular contact and work with others everyone would know, who would be glad to not only help with your situation, but with intros and promotion, if the material is strong.
Russ
[This message has been edited by captain Russ (edited 12-16-2010).]