Nothing that would be very effective, no. We can sign all the contracts in the world, but they are hardly binding. And any magical oath would be within your power, there is no saying you could not go back on your word while I was bound by my own. So all I suppose I can ask for is an act of good will. A favor. One to be procured at my leisure. One without price. Anything within your power that will not bring harm or risk exposure of your person.

[ Something against someone, more than likely. Like the devil. Or someone else. Baelish doesn't have particulars in mind, but he's sure there will come a day when he does need this sort of favor from the strongest magic user in this world. And he wishes to pass that price of magic onto someone else. Surely that would be within Peter Pan's power. ]