Pro cheat, get some beef fat from the locker to mix back in if grinding burger.
Our processor actually grinds up beef brisket to mix with the burger. I think he does 2 lbs of deer to 1 lb beef. He calls it a 50% mix, which I initially thought meant 1 to 1. But he explained it to me a couple years ago that it means the brisket is 50% of the weight of the deer meat.
I remember my dad teaching me that it's better to lose some meat than to leave any of the deer fat. I don't think I've ever actually tasted deer fat.
That infected shoulder sounds disgusting. How did the rest of the meat turn out?