I know at least one of Rush's former fill-in hosts in the western U.S. used to fly to Los Angeles to do his subbing.
I don't think it's the historic status of WABC as "Rush's flagship" that sent WISN's Mark Belling to NYC, it was probably that they wanted a network control room for him (so they were not subject to the whims and occasional glitches in ISDN fill-in).
I don't think it's the historic status of WABC as "Rush's flagship" that sent WISN's Mark Belling to NYC, it was probably that they wanted a network control room for him (so they were not subject to the whims and occasional glitches in ISDN fill-in).