It has been common place here in Edmonton between CHED and CHQT ever since CHQT became iNews880.
Advertising a radio station you don't own was a hot topic in the early 1970s (and perhaps earlier) in Vancouver when one station tried to buy advertising on several others. It was, at best, short lived, so I don't remember the details anymore.
Then, of course, there was JB Sha(y)ne who liked to make references to other stations on the air. I'm sure he wasn't being bribed by any other station, but it did make good comedy material. From simple things like remarking about "another station" on CFUN when the temperature was 73 degrees to full blown comedy bits on CKLG all nights, imitating CKNW's Garden Show host.
The ultimate in that vein, however, was
Lan Roberts on Seattle's KOL, playing a full length single of jingle singers doing KJR. Hard to believe that we are just days away from the 10th anniversary of Lan's death.