That seems difficult. How about bypass pay instead? I know everybody wants to be a CA, but the pain is a lot less, when your making more than the street CA next to you... Kinda like, any FO that "Could" hold the spot a street CA is in, be it age, TT, time with company, that bids it, will get CA pay for his longevity.
So, the number 1 fo, who is on the Q bids Q CA... because there are street CA's on the Q, the FO, while not upgraded should receive 4th yr CA pay untill he upgrades or bids different equipment. In turn, if he bid SAAB CA, and there were less senior pilots holding a spot that he could take, he would get 4th yr saab CA pay. etc ( I am very sure, that He would love 4th year ca pay while being an FO... sched of his choice, and high pay for his seat...)