Anonymous cofounder

so i have been internet friends with this guy for some years, now i want to do some stuff with him mainly for educational purposes but... imagine it actually turns out profitable. i can't think of a way to share profits and keep trust. i can imagine paying him via paypal but measuring how much he contributed would be hard. i am leading the project, have more experience etc.

at first i though i'd share all access to servers and all to maintain trust (i haven't actually done it yet) but our relationship is such that nothing stops him from taking over everything and locking me out of my own system :)

i think the best way to go on would be to stay solo, keep him as a freelancer and pay him based on some work he completes (paying only if what we build turns out to be profitable)

any thoughts?