Hmm this is quite tricky.

So when you pay 100% of his entry fee for a regular MTT if he cashes he refunds the entry fee and gives you back 70% of the excess?

He isn't risking any more money here but is putting in more time. You aren't directly funding the entire but are giving him 2 chances to qualify.

Let's pretend for a second that the satellite is a cash MTT. If he 'wins' he will get T$320.
If he refunded the $48 and gave you 70% of the excess that would mean he has 'earned' 25% equity in the WCOOP Event Buy-In after refunding one satellite entry.

Now if you staked the whole of the WCOOP Event Buy-In you would expect a refund of the $320 Buy-In and a 70% share of the excess. Here the satellite buy-in has been refunded already and you have effectively staked 75% of the buy-in. So you should expect 70%x75% of any winnings = 52.5%. If you wanted to adjust to account for a refund of the other satellite fee then $48 could come off first.