Don't know Margo, but my daughter shares the same "problem", however, when she "lets er rip", suddenly the audiences attention is riveted to her music and not her breast.

It really bothered her, at first, but she finally adopted the following attitude:

If you're playing to the point where the drool is comin' out of your mouth, who gives a shit whether they are looking at your breast or not, at least you are enjoying it and if the audience is seeking cheap thrills, let em.