Mode-local Defining keys for modes that are missing mode-local key-maps

[Nordlöw]

I am looking for a way to replace this little snippet in pnw-uni-
complete.el

  (global-unset-key [(tab)])
  (define-prefix-command 'uni-complete-map nil "Complete")

  (define-key uni-complete-map [(tab)] 'pnw/uni-complete-or-
indent) ;Note: Easiest to press: My Unified version.
  (define-key uni-complete-map [(i)] 'indent-for-tab-command) ;Indent
  (define-key uni-complete-map [(w)] 'fixup-whitespace)   ;in-Code
Indentation
  ...

  (define-key makefile-mode-map [(tab)] 'uni-complete-map)
  ;;(define-key autoconf-mode-map [(tab)] 'uni-complete-map)
  (define-key lisp-mode-map [(tab)] 'uni-complete-map)

with a way that also works for modes that doesn't provide an own local
key-map, for example autoconf-mode.el.

Is there such a way or is it easier patch these modes that are missing
it?

/Nordöw