I would try trot poles with X's thrown into the mix. That way he gets the hang of the rhythm and motion, and if he seems to master the X, raise it with the trot poles still in place. You could also set up a gymnastic line set for two trot strides in between, and place trot poles in between each jump.
You can mess around with this, but the idea is still the same. Trot poles REALLY help, and after a while you can take them away and he'll probably still get where to put his feet and how to get over the jump at a trot.
It's so funny, but I'm sure everyone - or most - started trotting jumps before cantering them. Even so, I'm sure I'm not alone when I say now that I'm used to cantering bigger jumps, trotting seems so much more awkward and even difficult at times. I always feel like I look stupid!
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