Quote Originally Posted by Xzin
You can kind of do that with PS/2 X-keys. They all act as one giant keyboard as they have pass through ports. You can daisy chain a foot pedal set to it and use those as modifier keys. I don't exactly understand what you want but it seems like what you want to do is already doable with the modular X-keys setup and/or some USB multicasters if you want to go the USB route.
I will have to read up more on X-keys.... I have to admit I never really looked at that.