I don't attach it at all. I just hang it over the side. It will not work at anything faster than trolling motor speed, but that is all I power my jon with. You might make a shaft attached to a C Clamp with the transducer mounted on the end. But, again, that would not work at cruising speed.
You might want to give Rickie of Podunk Ideas (rnvinc) a holler and see if he can come up with a movable mount. He is a wizard with that sort of thing. Check his website (below) to see some of the mounts he makes. He maybe able to modify one he already has. Look at the Da Ducer mount.
Podunk Ideas