I transplanted late one year as I ran out of money and larger pots one summer. Had a few plants root bound with leaves. It was right before flower though. In bigger pots they improved in days. As the other poster said, he can be done.
It's easy too. Let the pot try out a bit, the soil will contract and should slide right out of the pot when upside down.
I'm assuming your in less than 5 gallon pots right now which is the problem.