Is there some software I could use in gnome to emulate emacs prefix keys?

My idea would be to bind it to, say, “C-Super-X” and then the program would wait for my next keystroke… Depending on my next keystroke, some action would be done.

A little bit like “read -sn 1” in bash.

I suppose a bash script would be impractical, since it would only work if the mouse happened to be over the terminal window… maybe forcing the terminal to full screen… Also it might be too slow.