I've done this trick before:
Take a stick of 3/4" rigid, smash down one end like a point. Using a Hilti and a ground rod driver bit, I was able to "hammer" the rigid under a driveway. I did use duct tape on the threads of the end you are hammer drilling for fear of not getting the next piece screwed on. It worked fine with a little muscle behind it.
Once you get it through, cut off the end you smashed down, I put a rigid compression connector on it.
Dnk......
