He may be allowed to transfer his probation without having paid all the fines, which he would still have to pay. His first step would be checking with his PO to see if they are amenable to such a transfer. Then NC would have to be contacted to see if they would accept the transfer.
What the answer to both those questions would be depends on how long he's been on probation, what for, his relationship with his PO and any of a number of other factors.

