When I got my 2 florida gars, they had eaten live only, up to that point. Within a week I had them eating earthworms and krill. I bought some wooden tongs and dangle the food in front of their faces and shake it around a little. After about a month of this, I started to slow down on the krill (worked the earthworms out completely) and started adding jumbo food sticks. Now, they will eat almost anything that floats, but they still get the krill as a treat every now and again. I think that the tongs were the key to making this work. It takes time and patience, but it is possible!
I can imagine that gar can be fickle, they don't really get all that excited at feeding time like Oscars or bass IME. It was easy to train my fish, good luck with yours.