You should first check to see if your dish setup has a third output from the lnb (the eye on the dish facing the reflector) and run the new coax from there, if there isn't one, you then need a switch (preferably a DPP44 switch. The current outputs from the lnb would need to be run to the switch and the coax runs (including the new line) would then need to be run from the switch instead of the lnb.