You are not alone. I've contemplated doing this more than a few times. There is enough material on the lower to drill it out for the pin plus the material along the side of the receiver is thick enough to drill out for the detent pin and spring.
The only thing that keeps holding me back is the thought of how week the lug on the upper might become once that second hole is drilled cross ways through it.
If there was a way to fill the hole in the upper lug for the original bolt permanently prior to drilling the new hole cross ways it would be better but no matter how you do it I still think the strength would be compromised.
But just like your receiver, mine is also holding great with a nord-lock. The bolt takedown is just more of an inconvenience than it is a real problem.
Maybe once all my MS receivers arrive I will get brave and turn my SLR into a test dummy.
You guys are not alone about attempting it.
How about inserting some kind of soft threaded rod into the block before side drilling?



















































