You have to use a very large gauge needle. I developed that method way back in the late sixties, early seventies. Go to a feed store, they have them for horses.
I would enter between the second scale row on the sides. Personally I think it may be more difficult with hogs as they tend to harden up their bodies. I never had to do it with hogs, but even palpating them is not so easy as with kings and other colubrids.
You isolate the egg between your fingers, but do not put to much pressure on the egg, you do not want it to rupture. Best wishs and all the luck and skill