Key Editor: input notes for more then one part at the same time

Imagine I have two MIDI tracks, each one receives input from a different MIDI port, so I can affectively play both of them at the same time. (And each one will receive a different input)
This works great while recording in the project zone, but not so great when trying to input (or record) notes with the key editor.
I can open both parts in the key editor and see both of them, but only one can be active (and edited) at a time.
I get that this sometimes makes sense, but I wish there was a way to change this setting and enable me to input for both parts at the same time inside the key editor.
Does anyone know of a way to accomplish that?