One easy and relatively inexpensive solution would be to attach external sail track
to the mast. Then have your sailmaker construct your sail with sail slides
to fit the track. You can leave it loose-footed since it will only be a steadying sail at best on a trawler. That way you won't have to install track on the boom, and you will only have half the materials and a little less labor on the sail.
No boom, no problem as can be seen on Mark's Carquinez Coot
You have lot's of options. I'll bet a short visit to a local sailmaker will be worth your time.
Good luck with your project.