Hmmm.
I have a Securifi door sensor that is positioned close to the slave Almond. To pair it, I had to physically get the door sensor close to the master Almond, pair it, then go attach it to the door that is close to the slave Almond. Kind of a convoluted process, but mission accomplished.
I suppose I could attempt the same 'work around' with the light switch and dongle (assuming I can figure out how to get a neutral wire pulled back to that part of the building).
Or, I'm not sure there's a reason why I can't swap the positions of the master and the slave Almonds - all the 'smart' devices are back where the slave is, anyway. Maybe I'll do that, instead.