How to rebind quick-split in Rust (middle mouse button)?

[Stirfdogg]

My middle mouse button just stopped working, and for every game that required it, I just rebound it to the side mouse buttons (mouse4, mouse5) but Rust doesn't have this option to rebind it unless you can rebind it in console like you can with "bind q attack" for example. How would I go about rebinding the key to something else without using a macro program like AutoHotKey or something?