After some little misunderstandings I finally reworked my patch.
I tried to use the hints field of the location structure but it turned out (too late, already rewrote quite much) that this won't work if a location is not available.
(In that case an error struct is returned and I didn't feel it was a good idea to put a hint field in there. I think it's better structured this way since a method-spec is not really an extra info for a location. I'd rather suggest adding a general item-info structure if there's more information going to be added. --Nevertheless, in case you prefer adding the hint-property to the error struct I still could send the diff for this other approach.)
So I only changed the keybinding to C-k (according to a suggestion by Sean O'Rourke) and make it remove the corresponding line.
Andreas' suggestion of a dired-like behaviour is also nice but I think the current way it works is sufficient.
Still we need some testing for SBCL (haven't used my linux for quite a while) and backend support for all implementations other than Allegro 6.2 for win32.
regards
-ts