yeah its kinda annoying that you can't offer them something first. I have never persuaded someone to join who doesn't want to. Your best bet is to win some trophies and hope he'll want to join.
Get a Director of Football with a high rep, more often than not they are able to offer a contract and at a decent wage too!
You can then use "change contract offer" to check what he's offering and make sure there aren't any silly clauses in there.