If he had an empty forage pond, throwing in a half dozen male/female BG along with a single female GSF would get him all the hybrids he would need.
Pick some really good looking brood stock.
I know this is not a modern day stocking preferred method. But if you look up some of the old 60's and 70's research papers back when farm ponds were more looked at as a food source rather than a recreation source and commercial stocking fish were not nearly as readily available it was common. The way they did it in the old days may not be the way to do it for sportfishing trophys, but I bet it still works to produce fish.
Here is an example of an old study using parentals for stocking. PDF download.
RESxGSF hybrid potential 
