When I replaced my timing chains, I naturally had to remove the alternator as part of the job.
It is a surprisingly tight fit in there, and a real pain to remove/replace.
However, from what I can remember, there should be plenty of room to drill it out once the alternator is removed.
Sure, they might have to use a right angle drill and some stubby drill bits, but I can't say it is too difficult. More just a PITA.
This sounds like a "we don't want to deal with it unless you pay us stupid money".
Of course, if you can get one of the bolts tightened down and JB Weld/tack weld/some other shady attachment, that might be the route to go.
I don't think it's under too much stress once it is in place. Some side load from the belt tensioner, but the bolts don't hold that strain. They just hold it close to the block.
Heck, the one bolt is probably good enough.