Create rule in makefile for just a set of files

I am writing a Makefile, and I want to use a generic rule with wildcards, like

%: bkp/%
    cp $< $@

But I wanted this rule to be valid only for a few specific files. I wanted to define a variable with the list, for example

file_list = foo.c bar.c zzz.c

and configure the rule so it is only valid for files that are listed in this variable. How do I do that?