There are other alternatives to JA using the Standing Available list.
EX 1: I'll take that at MUP and you drop this with pay.
EX 2: I'm available for these other bases too. So, when JAs come around I'm the last one called. Let's make a deal.

If the schedulers are desperate or lazy, opportunities present themselves especially if you are creative. Straight pay - no thanks for me, but sadly I understand why a 1st year FO might do it.