Good to hear they make it easy... I plan on doing the same thing in July. 
It's too bad there isn't a way to make a payment to only the purchase part of a Discover balance, otherwise I could hold off until October. Rather than try to 'work around' the problem, it's easier to just transfer everything (remaining purchase balance and existing BT) in July and simply be done with it... LOL.
I'll have no problem paying the balance in full by July 2017 anyway.