Channel Aftertouch acts exactly like a continuous controller, and can indeed be assigned to Kontakt (presumably Giga too?), but its actual protocol is outside the set of "regular" controllers 0-127, but usually appears separately in menus by its actual name .."aftertouch"!
I don't have my Giga machine on right now, but I seem to remember a parameter for AT. It's not one of the #1-=126 ccs allowed, has a different header, but behaves the same, and I am pretty sure Giga can handle it, though it may require a separate dimension.
------- It's all about the music - really. I keep telling myself that...