Ok
First you will need to decide where to locate the traveler. It seems the hatch is in the way. You have an advantage that the mainsheet is end of boom. The forces to control the boom are less and the boom can easily handle the connection of the mainsheet. Your present set up gives you a 3-1 power. I suspect that is adequate.
Moving the system "to where" is the key. What do you have in mind?
I am guessing you might be able to put a bridge traveler on the seats in front of the stern hatch. Not sure if that would conflict with the tiller. You would have to experiment. Garhauer Marine makes some travelers that are designed to bridge a gap - like from seat to seat. The seats give you a solid location to locate the bases and the backing plates to handle the stresses. I would contact them and describe your needs.
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Harken would be my other suggestion.
You might find a resource right here at the SBO Shop.