I decided not to disable the thermal cut out or fuse, as I'd prefer to keep these safety features. Instead, I drilled some ventilation holes into the bottom and side of the boiler, and raised it up on bricks when boiling, to encourage airflow. By drilling the extra holes in the side (they're about as high up as they can be without drilling into the boiler section), I hoped that natural convection would draw air through the bottom and out the side. It seems to work, as I've now done two brews with it and not had a repeat of the problem (except in the last few minutes of the most recent brew, but it was a black beer and there was some residue on the element when I went to clean it).
Hope this information is useful!
Holes in the bottom (there's actually 4x7 holes):

Side:
