An idea: I could position the bike on the opposite side to which I'll have to get off the boat when cruising. That should prevent it getting in the way, I think?
THE TOWPATH ISN'T ALWAYS ON THE SAME SIDE, SO YOU WOULD BE MOVING THE BIKE LOTS OF TIMES!
Regarding locks: I could find somewhere before the locks to remove the bike from the boat, and the canal towpath. Proceed through locks, stop somewhere, walk back, get bike and ride it by road back to where I left the boat. This won't always be easy because access points for motorbikes aren't everywhere, but they do exist.
FIRSTLY THERE HAS TO BE SOMEWHERE SUITABLE FOR YOU TO GET THE BIKE OFF, WHICH MIGHT NOT ALWAYS HAPPEN.
SECONDLY, YOU AREN'T ALLOWED TO LEAVE YOUR BOAT ON LOCK LANDINGS, OTHER THAN WHEN WORKING THE LOCK. MOVING YOUR BIKE AROUND IS NOT WORKING THE LOCK.
Do think think that plan would make transporting it on the cruiser deck safe?
NO. SEE ABOVE!
PLEASE ACCEPT WHAT PEOPLE HERE ARE TELLING YOU, AS MANY OF THEM HAVE A LOT OF EXPERIENCE. THE ONLY SAFE PLACE FOR YOUR BIKE IS WELL OUT OF THE WAY, WHICH MEANS IT WILL BE BEST AT THE FRONT, SO A TUG DECK OR A BOAT WITH A LARGE WELL DECK. OTHERS HAVE DONE IT THAT WAY.