here is my take...
a delicious wordplay
Bull can obviously can mean an animal or a 'bull market'. Merrill Lynch's logo is a bull and I believe they are out of New York...
http://www.adversityuniversityblog.c...y-travis-s.jpg
Heather is the plant which is quite common around this time of year.
http://cache.eb.com/eb/image?id=95251&rendTypeId=4
So a bull in the Heather is an aggressive animal waiting to pounce.
The second meaning is presumably related to American hyperized sexual roles. Whether it be quartback and cheerleader roles, or banker and submissive roles. 'Betting' on the bull in the heather seems to acknowledge the inevitably of these two forces colliding. The phrase also seems to infer that there isn't much more to these people than the roles they play.
Heather is obvioulsy a name for a girl. The whole phrase is even more amzing when you see an animal lurking in the wilds. It gives the phrase a greater meaning...
You don't need and incredible imagination to know what 'in' means