well heres the deal, a good keeper male is like a good keeper female, more seeds u put down the better chance u have to find one. Your problem is the opposite of just about everyone i know, they want more females and complain about how many males. IMO, Keep planting seeds.
If you stress the seed in its germination stage, it will most likely become a male. But you only need to get 1 good male of something, unless you want to go cross crazy...
Other than stressing the plant in its earliest stages, I dont know of any way to make a male-its against everything i know lol- I just happen upon them occasionally and keep them if they look healthy.