Don't do it.
It may seem like a smart idea to put an A/B switcher in so that you can control what's coming into your entertainment center. The problem is, it doesn't work.
I recently worked with a customer who wanted to use the wiring in his RV for satellite, cable TV and antenna use. He was only going to use one at a time, so he had the idea that he could use a switcher to control which source was in use, and then split the signal out to his TV and satellite receiver on the other end.
The problem here is that there simply isn't an A/B switcher that's designed to work with satellite. In some cases, your satellite signal carries voltage that could instantly fry that switch, and even in a best case scenario the hardware on the inside of a typical A/B switch isn't going to handle the high-frequency signals used by satellite TV. It isn't designed for it, and that means that you'll get poor reception and a lot of signal errors.
This sort of request comes up because with DIRECTV's SWM technology, it's almost impossible to diplex an antenna signal in with a satellite signal. It used to be a fairly trivial matter but now it's just not allowed, because the frequencies used in antenna TV interfere with the signal that allows you to share programming between receivers.
So, folks, the only good solution here is to run more than one cable. I know that can mean a lot of time and money, but it's really your only choice for reliable satellite TV reception.