I doubt the bolt can be drilled; it will probably just spin unless one can grab the edges with needle nose vice grips to hold it in place. If so you might be able to drill the head off by gradually increasing bit size. AFTERTHOUGHT - I wonder if you could center mark the bolt head; then use a combination of a socket and vice grips to hold the bolt; insert bit thru socket and carefully find the center mark then drill - not sure how well that would work but it might be better that cutting off.
After a bit of poking around I found that the retaining nut is in a silly plastic thing on the front of the TCM plug in so my notion of access from the back is a no go. Geordi suggests (I cannot find that old LOST post I mentioned above) carefully cutting the head off the bolt with a dremel cutoff wheel. There is not much clearance from the TCM pins (see
viewtopic.php?f=5&t=28916&start=20) so you might want to gently cut into the plastic around the bolt so you can see what you are doing before trying to cut off the bolt head.
NOTE the bolt really is not needed to retain the electrical plug as it's a really tight fit.