prefix key with its own map as binding?

[Joost Kremers]

is there a "conventional" way of binding a prefix key to the very same
keymap it is in? basically thus:

(defvar some-mode-map (make-keymap))
(suppress-keymap some-mode-map)
(define-key some-mode-map "a" 'some-function)
(define-key some-mode-map "b" 'some-other-function)
(define-key some-mode-map "c" 'yet-some-other-function)
(define-key some-mode-map ...)
(define-key some-mode-map ":" 'some-mode-map)

(fset 'some-mode-map some-mode-map)

the idea is that every function that is bound to a key in some-mode-map can
be called either by pressing its command key, or by pressing `:' followed
by its command key. the function called can then use this-command-keys to
determine how it was called, and determine its behaviour accordingly.

alternatively, if all this sounds like A Bad Idea(TM), is there another way
to get this (or similar) behaviour? (using a prefix argument is not really
an option, btw.)

TIA

-- 
Joost Kremers                                      joostkremers@yahoo.com
Selbst in die Unterwelt dringt durch Spalten Licht
EN:SiS(9)