One tool that does a bit the same job of a carpet knee kicker is a carpet stretcher.
This device has two long poles hinged together. You grab the carpet on both sides of the room and then expand the long poles by the hinging action. This will force a carpet straight or even put it under pressure.Check your rental tool store to see what they have available.
The knee kicker is the quick and easy tool for forcing the carpet into a corner, usually onto a nail rack. The secret is to not hit the pad with your knee, but a fair bit above the knee, hitting the pad with the upper leg bone. The lower leg serves as mass momentum to move everything forward.
Now let's see. If we really want to get inventive, we could probably use any hammer action type of tool attached to the end of the knee kicker in place of the soft pad. Something like a pneumatic palm nailer, or a hammer chisel. That would give you the forward pounding action without using your knees. Then you need to invent some way to do that standing up to completely get off of your knees. Don't forget to control it or you it or you may tear your rug apart! Any ambitious inventors out there?
That was written in 2001 -- and in 2004 we got a response.