Q: "How can I use compression on my final stereo mix that will affect the vocals and not the drums?"

Compression on your final mix is an art that many mastering engineers have been able to hang their hat on. In other words, it's not the easiest thing to master (pun intended). There's really no way to do anything to the stereo mix without it having some effect on all the elements. With that said, you can sometimes manipulate things in ways that can emphasize certain aspects of a recording while not causing too much harm to others. The secret to this with compression comes from understanding the attack and release parameters. The basic idea is that fast attack compression will usually help to tame drums on stereo masters, while slower attack settings tend to affect vocals and other similar instruments (bass, strings, etc.). Just how fast or slow depends a lot on the specific instruments and how they are mixed. There's simply no hard rule on this, to get started you can turn up a pretty extreme amount of compression and play with the attack and release controls. You'll begin to be able to hear how different elements are changed by the compression. Once you get close to understanding the attack and release times that change the vocals while not killing the attack of the drums you can dial it back to a more reasonable setting and go from there. It's all about experimentation.