David, as others have said there's not much you can do, other than when you bring it in, cut it down and do the short standard thing with it so it's not so gangly. It will take up less space through the winter that way, too.
I've had some that Y'd at 3ft. and one, I think it is a Frosty that went up 7ft. and took 2 years before it finally Y'd. It's a 9ft. tree now.
I've had cuttings bloom while still rooting in water too. Ya just never know with these plants, it probably varies by type. Some are more vigorous than others, make bigger leaves, bloom more often, smell different, have bigger flowers etc. etc. This one, Monster White, I got as a 10in. cutting in spring 2012, and by July it was a 3ft shrub with 25 flowers.
On the other hand, I paid a fortune from Logee's for a start of a variegated one, got a very small plant, coddled and loved it, potted it up, then finally put it in the ground in desperation and it just never put on a single new leaf. Not one.
