EPM Template Variables in BLF Line Settings

I seam to remember it being discussed here before but my search isn’t finding it.

How do I setup a BLF to contain variables, ie, i’m trying to setup a BLF to login/out of queue 1000
So i defined a BLF button in EPM for 451001000 with works great for extension 100 but how do i apply this to the entire template so that it follows *45__line1ext___*1000
I can do this in base files but would rather do it in the template if possible.

Just set that as yoru BLF value. When we write out the config we replace line1ext with each extensions line 1 value.