50/50 is an arbitrary number.
You should ask him how much is fair and find out what the expected hourly is after cover/err estimates. I'm just barely comfortable with my bankroll and my friend wants to play on it. I am not so comfortable that banking him that splitting 50/50 would compensate my risk, but a move down in stakes to pay 50/50 would make us both worse off (worse/crowded games etc). Someone with a bankroll, bj understanding and trust is rare. I am such an asset to him that he'd play with a 15/85 deal. He's good and reliable (ie an asset to me) that if I had a big enough bankroll id be willing to spot him 85/15, its free money. So anywhere inbetween could be fair depending circumstances, paying more for travel and less for local (higher cover) and what my bankroll is. This is probably only a little more exagerated than what most compensation decisions are like. However my bankroll has taken some hits and I'm considering bj full time making preservation even more important. So much so that even though we have such a good arrangement, the risk burden is so high that my choice is between terminating any deal or paying less, etc.
Generally you should put a player into the biggest game you can afford to lose at. As the sole bearer of risk with a limited bankroll, it makes sense to pay a lower hourly but give raises or bonuses(retropay) based on performance/variance as an increase in bankroll increases your abilty to stand risk which should raise ur willingness to pay.
My player won a bunch of money early so I payed out extra. Since then we've had some negative variance and now I think cover should be given more consideration so I'm paying less/hr but with the expectation of getting more hours in.
Afterthought: Clarifying such a dynamic compensation may help in reducing skimming/stealing since they will see how their fate is more closely tied to yours. However I wouldn't. Enter into a deal with anyone I thought would steal to begin with.