you can't. Multiple-friends slots is a violation of what the developers have asked the modders not to implement. Sure that hasn't stopped neomule adding other features that are questionable, but it looks like its playing ball with friends slots
Other mods do have this, MorphXT allows multiple friends slots, but it doesn't include this in your ratio, so if you over use it, and don't give enough b/w to your other slots, then you'll hit the inbuilt 1:3 up/down ratio
but does anyone know how to set it up so you can have more than one friendslot at once? 
