A guy posted an interesting question on stackoverflow:
Most emacs modes include some sort of prefix to activate their features. For example, when using GUD "next" is "C-c C-n". Of these modes, many provide special buffers where one can use a single key to activate some functionality (just 'n' or 'p' to read next/previous mail in GNUS for example).
Not all modes provide such a buffer, however, and repeatedly typing the prefix can be tiresome. Is there a well-known bit of elisp that will allow for ad-hoc specification of prefix keys to be perpended to all input for some time? (Until hitting ESC or some other sanctioned key, for example)
I don't think you want that (in general) because many of the prefix commands contain an extensive set bindings which clobber too many useful keys. That being said, I'm sure there are places this could come in handy.
I wrote up a solution that prompts you for a key sequence, and it promotes the prefix command keymap to the toplevel (associated with this particular minor mode). The minor mode is buffer specific, and it only allows one prefix command to be promoted at a time.
Check out my answer (won't put the code here in case I need to make an update).