I think you may just want to start by pruning the top some to see if you can get some buds to pop down lower on the trunk. But, not all JRM's are good for bonsai. Varities like the laceleaf kind have leaves that do not really reduce too well.

If it's capable of surviving on it's own roots in your zone, without a graft, I'd say air-layer it below the first branch and have two trees! Though, I believe I remember reading somewhere that certain JMs do not airlayer well.... Or was it cuttings that are a pain?

I'm sure someone will be along shortly with better advice.

-Froz

I don't know the exact variety. I'll post a pic later.

Sorry for poor quality of pictures. Note one gangly top branch and fuller mid-branches. I think wiring down the top and using the mid section as the top would be most appealing

Here is a link that might be useful: JRM pics