Here's what I've got that works:

### External.pm
package External;

use strict;

use base qw(Exporter);
use vars qw(@EXPORT);
@EXPORT = qw(external);

sub external {
    print "I'm in the external package!\n";
}

1;

### Foo.pm
package Foo;

use strict;

use External;

use base qw(Exporter);
use vars qw(@EXPORT);
push @EXPORT, @External::EXPORT;

sub from_base {
    print "In base...\n";
    external();
    print "Done in base...\n";
}

1;

### Bar.pm
package Bar;

use strict;

use Foo;
use vars qw(@ISA);
@ISA = qw(Foo);

#use base qw(Foo);

my $x = bless { }, 'Bar';

$x->from_base();
external();

1;

### base-tester
#!/usr/bin/perl -w

use strict;

use Bar;

print "Done\n";
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With the above bits, I get the correct behavior - which is to say that I can access external() from Bar.pm. However, if I comment out the lines for use Foo;, use vars..., and @ISA... and uncomment use base qw(Foo);, it breaks.

tye had suggested looking into Exporter's export_to_level() or re-calling import, except the idea is to, ideally, need the fewest moving parts in Foo.pm (and none at all in Bar.pm).

And, yes, I'm aware of Spiffy, but I'd prefer something that's a little lighter-weight.

Thoughts, comments, suggestions?