Is there a way to use the jam cleat on top of the boom whilst keeping the rotation bar in the stock location?
That is exactly what I did on my boat. I will try to describe as best as possible how I did it...
Use a large diameter line to secure a bullet block to the rotation grommet in the center of the tramp. The line has to be large enough so that you can tie a stopper knot (8-knot) in each end and it will not pull through the grommet (i.e., tie an 8 knot in one end, then feed the line up from under the tramp, pass the line through the becket in the bullet block, then feed the line back down through the grommet and tie an 8 knot in the other end).
Take a smaller line (1/8" to 3/16" diameter) and tie off to the end of the rotation bar. Route the line back to the pulley you tied to the center tramp grommet. Then route the line back to the rotation bar and feed it through the "hoop" in the end of the rotation bar. Continue routing the line forward to the center sheave at the mast base (the main halyard sheave). I believe we pulled the main halyard out of the sheave and stuffed it in the tramp pocket first. Then route the rotation line up the mast and feed behind the gooseneck fitting which is riveted to the mast (i.e. your rotation line will actually be fed into the sail track). Mount a micro block to the mast track slightly above the gooseneck fitting. Pass the rotation line out of the sail track and through this block and then lead the roation line back to the cleat on the top of the boom.
This is not the easiest system to rig because you have to unthread your main halyard line from the bottom sheave and you have to feed the rotation line inside the sail track. However I recall it worked just fine and it didn't require any additional holes to be drilled in the mast.