The thing with getting Pacmans to eat different varieties I think is to 1)movement, 2) familiarity, and situationally, 3) desperation.

I got my pacman while he was still fairly small in his critter keeper, so I was more easily able to switch him to nightcrawlers; but since you've noted that he is quite big and his diet consisted of primarily crickets and occasional pinkie, it would be hard to get him to try nightcrawlers without starving him a few days. Luckily for me I had fed him crickets on his first two feedings in my possession (every 2 days). But when I wanted to introduce nightcrawlers I waited 3 days to feed him, before going back to the normal every other day schedule.

If you go a few days without feeding him, and can successfully get him to eat one worm on the next feeding, you can feed him more very easily.