Is there some way I can disable the overvoltage protection on these
power supplies?


Look up a datasheet for the controller chip and see how they do the
protection, it shouldn't be too hard to trace the circuit and disable it.

If it was that easy, I wouldn't ask. Those chips don't have a shutdown
pin or anything real obvious like that. I've spent a lot of time
looking at the datasheet and the circuit board.
I was looking for a germane response from somebody with hands-on
knowledge of the issue.