I didn't know the gunnel was a carbon fiber tube.
I can see why you wouldn't want to drill into that too.

That glued on wood wedge doesn't look very nice either.

I would try to go a different route, same principal.
Instead of gluing wood block to gunnel, I would find some thick rubber, cut into a wedge and glue/screw it to the portage yoke clamp.

Rubber clamped tight gives your more friction than the wood and you don't have to worry about the wood splitting or ruining the looks of your canoe.