I find that for most of my canes just giving them plenty of light will cause them to break from the ground. Some are more inclined to branch than others, and the breaks from the ground do a good job of filling any of them out. The ones that are not inclined to branch usually look funny when their tops are pinched (at least to my eye) but can get very full with a little time, plenty of light including at least some sun, and light fertilizing. If that's not fast enough. you could cut it to the ground (assuming it's well established) and stick the cutting back in the same pot. That way you would have at least two breaks from ground level and your new cutting, which would add up to a fuller plant sooner. (I'm more inclined to be patient and let them fill out themselves, but I recognize that sometimes we need a fuller plant sooner.)

Oh yeah, if they aren't inclined to branch it's impossible to force them, Nancy's a hundred percent right about that, and yes, they look really peculiar if they get tip pruned, they send one single branch out from just under where they were pruned that sticks out like a wild hair. NOT attactive!