As stupid/simple as this sounds, it generaly always ends up working for me with Gar.
I had about 200 minnows in quarenteen. I sectioned the gar off into a small area of my tank. I dumped 50 +/- in there with the gar. The next morning all were gone. I then dumped another 50 +/-. In a few hours came back, all were gone. I then started dropping in minnows one at a time and waited untill the last one was gone untill I added another. I did this for 2 days. By this point, the gar would come to the surface when I approached, ready to be fed. I then just started tossing in Hikari 5-10 sticks at a time. One by one they started taking them. Took about 2 days untill they all had eaten them. Suprisingly, the smallest one was the first to take, now they all eat them untill I stop feeding.
Floating Hikari Sticks by the way.