So I did some more digging, and I had totally forgotten that TASMOTA gives you the ability to flash over the air.
After a few minutes of debating whether it was worth it, I bit the bullet and flashed the custom firmware from here and followed the setup instructions from the ST forum post.
Everything worked great!
I would still like to know if it would be possible to do what my OP was asking, but now it's just a nice to know rather than a need to know 
Cheers to @ericm for the firmware! I will say that I ended up adding the sonoff manually via the IP address. Do I need to reserve that IP now or will the app driver switch to using the MAC in the future?
