ahhh .... so this is the Banana Technique (I avoid religion like the plague
)
So what is it ... the off gassing ethylene of ripening bananas that promotes the female gender? This should be interesting .... I'll certainly give it a try, what harm can it do? Other than attracting fruit flies I suppose
Do you shut down your ventilation fan for the banana duration? I would think with a fan blowing about, the ethylene would just be blown away .... dissipated into the air, therefore not effective at all
Perhaps a less direct approach to ventilation .... throttle the fan way down, and point it away from the plants. Think that will work?
Well .... off to smoke a joint, then on to the monumental task of peeling potatoes
Seize the day everyone ....
Happy Thanksgiving! 
jv