Just for the record, I found the flaw in this scheme. One of my included modules includes 'Storable', which tries to include 'Log::Agent'. If it fails then the 'Storable' module does something else. The above @INC scheme forces the user to install the conditional module. This shouldn't happen.

So back to the old method (slightly refined to handle module versions and import lists)

{
   our @missing =
         map +(m/^(\S+)/),
         grep !eval "use $_; 1",
         grep $_,
         split /\s*\n\s*/, "
              Storable
              File::Basename
              A::B wq(a b c)
              Foo::Bar
              CGI qw/:standard/
        " and die "Please install CPAN modules: cpan -i @missing\n";
}
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