Here is my suggestion... which is used alot with poker staking. And it honestly seems the best way.
Although most pool players will not like this, but if they are broke, then they cant be beggers and choosers both.
#1 The backer gets 50 percent, the player gets 50 percent.
If the player loses the stake, then the backer is owed the stake from any future scores before the staked player gets any money.
#2 Or you could go with just s 60/40 split and the backer getting 60% only. (if you are on the road, and paying for all expenses, then 65/35 or 70/30 for sure....... dont be a sucker, if they don't like it, tell them to find someone who is a sucker)
I personally do not like to back pool players, because they expect to much even though they are risking nothing.
If your the one asking them, and they are not asking you, you can decide to take on more risk, since you approached them. But for the most part all I have ever seen is a broke player wanting to get backed and take no risk at all and expect the world from you....
If I do back someone it will be system #1 above.