What seems like a simple task has turned out to be a real pain. I'm trying to configure line buttons on a 7914 sidecar that will simply light up when whatever phone it's configured with goes off hook.

I initially tried this with a shared line appearance. The problem with this is any incoming call to the configured line flashes on the phone's screen, even if the ring settings are set to "Disabled"

Next I tried to set up a BLF SD button ( saw "Busy Lamp" and got excited), however it doesn't light up when the phone is off hook.

Any ideas on how to accomplish this? Thanks in advance.