I always assumed that Fredo's "something" was a cut of the deal, once it was made on terms favorable to Roth. I mean a cash payout, which would be easily hidden from Michael.
I think it had to be more than a cash payout. Fredo probably had all the cash he needed. This was a promise of something important...something that carried power. Mike says to him
"I've always taken care of you." And Fredo isnt mad that he is taken care of he is mad that he is being taken care of by his younger brother, mad that he was passed over, mad that all he does is run mickey mouse night clubs and take people to the airport. I think the bait was more along the lines of Ola playing to Fredo's anger and saying Mike was being tough on the negotiations and that if Fredo helped him he would get power in return... he could even have told Fredo, "You're his older brother and look how he stepped over you. You are a valuable guy and your own family doesnt respect you. Now you have this chance to do something good for the family and in addition theres something else in it for you"
