Umbrella Plant

I've got an Umbrella Plant in the conservatory (well, three in a single pot - don't think they are the same plant).  When I bought it from Homebase three years ago, it was only 2 foot tall.  Now, it is over 9 foot tall and banging its head on the roof of the conservatory.  I have been trying to train it sideways, but its not happy, and I'm sure its going to be a pain to try and repot when know doubt it will get much bigger again.

I've been wondering if I prune it back to about half height, will it bud out side shoots, making it more bushy, or will it just stop and remain a 4 1/2 foot stump with leaves for the remainder of its natural life?  And what is the likely success of trying to root the bit I lop off?

Funny when I was in Canary Island a few years ago, I spotted they used Umbrella Plants as green planting in the central reservation of their roads.