Yep, that's what a contractor I was digging holes for did to mine... his digging bar/spud fit in a hole already in the gearbox. I've read of some welding a short piece of pipe (sleeve) onto the PHD to put a pipe in also.
I've dug a lot of holes with mine solo and if it won't dig, I lift it up, pull away from the hole and use my spud to break up the rock or brick that's stopping it. Sometimes inching the tractor in one direction or the other will give the auger a different angle of attack and get you on your way, too.
Wet ground is easier to dig than dry ground, so maybe you can wet the ground where you're digging, I've read that this is what you do if you're digging in clay.
Be careful.