Just to be clear,
I didn't mean to bell out the deepest portion of the hole. I can understand your hesitation at that notion.
When I referred to a ball mill I am only talking about like an 1/8" diameter or so burr like in a dremel kit. I would chuck it up real shallow and make a couple rings or grooves in the hole you have there. It may be totally unecessary with a good epoxy but certainly shouldn't be any more invasive than what you have done.
You have to be comfortable with your choice. I am just armchair quarterbacking it... I did however want to describe how small of an area I would relieve.
Then you can just use threaded rod for your studs and the epoxy would fill the threads, the grooves and be stronger than the spoiler itself.
