The problem with trimming these back is then you won't get flowers until two more growing seasons. When these plants bloom, they branch, giving you more tips, denser growth and more chances for blooms in the future.

So the REAL question is, why isn't yours blooming?

Perhaps it needs more sun (6+ hrs per day), more fertilzer (lower nitrogen though) or a larger pot (or all of the above). You could selectively prune back 1/2 of the longest branches leaving others to bloom next season. Then after the following season prune back the other half of the branches. Also, keep in mind that plumerias are TREES and can eventually get 20-30 feet tall or more in the tropics.

Also, some varieties (such as Aztec Gold) are just large, lanky growers. You may want to look for more compact varieties, such as 'Penang Peach' or Jungle Jack's Mini 'Divine'.

Or you may just have to get rid of some of the bananas and hibs to make your plumerias your priority! LOL!

Do your plumeria go dormant and loose their leaves, or do you try to keep them from going dormant by providing light and heat? If they go dormant, I'd stick your plumeria in a spare spot in your basement or other area that doesn't freeze, and basically forget about them, and bring them out in the light and heat in the Spring. I'm growing them under indoor plant lighting in a spare basement room, and keep the lights on about 20 hours during the day. They are growing just like during the summer.