Say you have a balance transfer at a low APR and purchases at a higher APR, all on the same bill. You make a minimum payment and it goes to the lower APR segment first. This drives you crazy, of course.
The way around it is to simply pay the minimum in your regular monthly payment.
THEN...make a second payment to the following address, putting your cc number on your check and specifying what segment of your bill you want it to go towards.
The special address is:
Exception Payment Processing
PO Box 183037
Columbus, OH 43218
I bet it's worth asking other card companies whether they have a procedure for designating a second monthly payment to go to a particular segment of your bill. Can't hurt to ask. And while you have them on the phone, talk to them about lowering the rate, especially if you've already got a balance transfer offer in hand.
I also found out that rather than convenience checks, ask for balance transfer checks made out directly to you. Far cheaper APR that way.
Of course this is part of my solution to abruptly leaving my job. Thank Goddess I have some credit behind me, even if I'd rather not use it this way.