Frets on Fire X: Can you play multiplayer with two guitars?

[Gmod4ever]

Simple question that I can't find asked or answered via Google searches.

If anyone has ever played Frets on Fire X (FoFiX) multiplayer, then you may or may not know the answer to this. I plugged in another USB keyboard (my primary keyboard is a USB keyboard as well), and I want to know if it is possible to play FoFiX multiplayer with two of us doing "guitar" parts (technically bass/guitar).

Going to multiplayer with default settings sets the second controller to drums, and both keyboards affect the guitar (AKA I can hold down buttons on my primary keyboard or the second keyboard and the game treats both as my primary keyboard)

Going to options and setting both controllers to guitar causes a conflict, which makes me think this isn't possible.

I suppose what I'm really asking is if there's a way to make the second keyboard act as a slave, and then can FoFiX pick up the slave and use it as controller two?

Thanks to anyone who can help. :buddy: