There is no way to increase just FO pay because "the union" gets greedy and wants to raise everyone's pay. The see F/O's get a $20/hr raise and they want the CA's to get that raise as well. It's ridiculous how big a disparity between seasoned F/O and junior CA there is.
That's why I suggest a track system, and the new hire would go on the higher pay to start/lower top out while everyone else remains on the original pay schedule they signed on with.