I'm guessing you're referring to the Gar as the consumer of the feeders....
It might be hard to do, but you might successfully wean him. The trouble with feeders is the risk of disease, as mentioned.
The thing with breeding your own is that you would want to keep them in ideal conditions for faster growth, plus the fact that you don't want to feed your fish nasty food and make him sick... Lots of work, but after an experience I had years ago with feeders, I consider it to be well worth the effort.
My live food eaters are small enough that I can feed them Ghost Shrimp, which from all I have found is safer. Plus they readily gobble frozen foods as well. This may not be an option for your fish though, I'm not that up on Gars and their dietary needs.