By the time you are transferring balances, the original vendor and account the charge was made for are immaterial.  I am not sure how you are processing the original charges but if you set up a Liability account for Credit Card Due then make it a dummy "checking account" and use it to pay the original vendor and post to the inventory or expense account.  Then that total liability in Credit Card Due doesn't really care which card it is against so there is really no transfer to be made.  Just post to that liability account when actually processing the check to pay a credit card.