trying to set nnmail-split-methods neatly

[Rafael Villarroel]

I would like to be able to define a string to be used in
nnmail-split-methods, as in:

(setq common-string "stuff")

(setq nnmail-split-methods
    '(("Foo" (concat common-string "more-stuff")
       "Foo2" (concat common-string "other-stuff")
       ("Misc" ""))))

but everything goes into Misc, even those mails that go into Foo when
I write that rule directly as ("Foo" "stuffmore-stuff").

I know the manual say that the second element can be a function, but I
think there should be some easier solution than maybe writing a
function for Foo, another for Foo2, etc.

so I kindly asks for suggestions, thanks in advance