Nope, sorry. You're going to have to run another line into your entertainment center. What you describe won't work for 2 reasons - first the switch is built into the dishpro twin or quad already. The only external switch that you would add would to be to combine the signals from your dish 500 with the signal from a sideslot satellite (61.5 or 148). Secondly, because what a switch does is combine the signals from 2 (or 3) different satellites into one output and then switches that output between the 2 or three satellites through the one line. You're trying to come up with a fancy way to split the one line coming in, and you just can't.
Also, based on your equipment description, you have an SW-21 switch installed up by your dish that the 1 line is coming out of now.
Also, based on your equipment description, you have an SW-21 switch installed up by your dish that the 1 line is coming out of now.