The standard practice in my chapter has been basically what would be considered a rush infraction. If we know someone who has considered going Greek but hasn't signed up for rush, we start rushing them.
Basically we start telling them how great we are and how ABC hazes like nothing and even the fraternity guys will tell you that XYZ is nothing but sluts. And why would would anyone want to be DFG, they'll circle your fat! "Oh and rush is a nightmare anyhow! You should just wait and do informal." (We've consistantly been the only ones even able to do COB.)
(But honestly we don't make up anything!)
So basically, I would have tried to get the guy/girl to have never even looked at the other house. But I guess this is one of those things that should fall into more of Do as I say not as I do!
The subliminal thing sounds good. But maybe you could suggest that the guy talk to sorority members! As we're always reminded in our workshops, "Fraternities and Sororities do not have the same Rush rules!!!" Basically you can't talk trash about the other house, but the girls can!