People are going to need a lot more details in order to give you a good answer here. What's the staking deal for? What games does this player usually play in? How much is he/she winning in those games? Etc.

You are right James! Its for a PLO Live Cashgame, Average winrate is between 500 and 1k per day...or around 100usd per hour

The Markups for Tournament players usually are done per tourney, so I was aking what you guys were thinking about bringing this idea to a cashgame...would a 10% markup persession be fair or too much? What are the parameters you guys would say that are important to measure the markup...Thanks a lot for all your thoughts, its highly appreciated...

50/50 SPLIT of profits with makeup if they are losing

I would rather go with salary based system.

If you are the one who can afford staking, then you can obviously handle variance better. If you know what is the estimated winnings for the night, for example 15 bb/100 for 250 hands, expected winnings are then 37,5 blinds.

From that you can pay for the cash-player let's say 20 blinds. You will keep the expected profit of 17,5 blinds but you must endure your variance. Actually I believe that the results are better if the player you are staking is 100% indifferent for results. That will most likely make him do more correct decisions and higher results for you too.

If it looks like that the salary is too low for the expected winrate, that can be easily adjustet later on for increasing salary for the next session. I think that it is much better if the results for the night won't change the salary however.