Critch,
I've heard quite a few good answers to this one - ready ?
(1) Tell him/her you are unhappy with this and remind them of the minima and that your concerns are being recorded on the voice recorder.
(2) Tell him/her if they wish to continue that it is illegal and you will have to file an ASR when you land.
ps Don't try to wrestle control of the aircraft.
I'm sure there are other answers with equal merit - hope this helps !