I mean, you are already "performing"; it's not as if it is computer-generated (or drawn with the mouse), so it should already be "humanized." I believe the real issue lies with subpar MIDI keyboards that lack sufficient responsiveness. This is rarely a problem for me with guitars, where I can always dial in velocities with exactly the precision I have in mind (and I'm an amateur).
FYI Another way MIDI is humanized in DAWs is in the temporal domain (i.e., rhythm/timing). This was popularized by Ableton's Groove Pool [1].