I believe this is called a designer estrogen. This sounds impossible to me. What is required is a medication that would switch on or off the effect of estrogen at different sites around a woman's body. An ideal drug of this type would do the right things on the right parts of the body and prevent the effect of estrogens on organs where estrogens could be harmful. Tamoxifen has some of these target-specific effects.
Tamoxifen also has an estrogenic effect that lowers cholesterol and preserves bone density.
However, it has been shown to expose its users to the risk of endometrial cancer and blood clots. Raloxifene, recently introduced in the market under the brand name Evista, has many of the properties just mentioned. This drug has just been approved for the prevention of osteoporosis. Scientists at drugmaker Eli Lilly found that raloxifene was almost exclusively an anti-estrogen in the uterus, exhibiting much lower ability to stimulate the uterus than does tamoxifen. Another group studying the effects of raloxifene on bone demonstrated that it was able to prevent bone loss.