Give it a go, Cut it right back.
If it dies, it doesnt matter if its ugly! Plant a new one.
I've butchered plenty of things and everything seems to grow back pretty good, maybe hold off for a month or until its a little bit cooler, but dont wait until things go dormant either, because then you'll be stuck with ugly trunks without leaves until spring.

Thanks so much, Bryan. It certainly isn't much use the way it is. I'll let you know how I go.

Well, did the deed the last week in April. Chopped back to a metre from the ground. No leaves now, apart from a few that were already sprouting low down. Cut out all the crossing branches and the ones sticking out too far into the lawn area. Plan is to keep the new growth well-trimmed and shapely, and for it to stay at about 3m. Will let you know how the experiment goes.

According to Burke's Backyard, Rondeletias can be grown from semi-hardwood taken in late October to November.

Here is a link that might be useful: Burke's Backyard Archives 2001 - Rondeletia

Sorry, I posted my follow-up to the wrong topic. Should have been to a question regarding growing from cuttings.

Well, it's August 2004 and the rondeletia has new little branches (about a metre in some spots) and even some flowers, so looks like the experiment worked. I'll prune after flowering and keep on top of it from now on. Thanks to everyone for their input.