eval "package $caller;";
    Foo::Core->import(@imports);
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I suppose this doesn't work because the package needs to be known at compile time...

Try this

eval "package $caller; Foo::Core->import(\@imports)";
[download]

Update: something like this works for me:

package Foo::Core;

use Exporter qw(import);

our @EXPORT_OK = qw(func_a);

sub func_a {
    print "in func_a(): @_\n";
}
1;

-----

package Foo::Core::Specialized;

use Foo::Core;

sub import {
    my $this_pkg = shift;
    my @imports = @_;

    foreach (my $i = 0; $i < scalar(@imports); $i++) {
        if ($imports[$i] eq 'Mixed') {
            print "doing something with 'Mixed'...\n";
            splice(@imports, $i--, 1);
        }
    }

    my $caller = caller();
    eval "package $caller; Foo::Core->import(\@imports)";
}
1;

-----

#!/usr/bin/perl

use Foo::Core::Specialized qw(Mixed func_a);

func_a(42, 'foo');


__END__
$ ./807805.pl
doing something with 'Mixed'...
in func_a(): 42 foo
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