Warning: Don't use the following *as is*, you might get beaten. But for the sake of TIMTOWTDY...
See note at the end.

I concur with Marshall, that having 500 symbols to export smells like a design flaw. But that must not be the case. You could use perl's subroutine of last resort - AUTOLOAD - and not export anything explicitly...

package MyConstants;

use strict;
our $AUTOLOAD;

sub import {
    my $package = shift;
    if ($_[0] eq 'AUTOLOAD') {
        my $caller = caller;
        no strict 'refs';
        *{$caller.'::AUTOLOAD'} = \&{$package.'::AUTOLOAD'};
    }
}

# Constants
use constant {
    NIL => 0,
    FOO => 1,
    BAR => 2,
};

sub AUTOLOAD {
    (my $func = $AUTOLOAD) =~ s/.*:://;
    no strict 'refs';
    *{$AUTOLOAD} = \&{__PACKAGE__.$func};
    goto &$func;
}
1;
[download]

#!/usr/bin/perl;

use MyConstants qw(AUTOLOAD);
use strict;

use constant { NIL => -1 };

my @ary = qw(ene mene muh);
print join(" => ", @ary[FOO(),NIL()]),$/;
__END__
mene => muh
[download]

... to get the constants when they are needed, at the expense of explicitly marking the constants as function calls (they are that anyways), e.g. FOO(), which otherwise would be interpreted as barewords.

But I myself would consider that bad practice, since it is too obscure. I'd use that technique only for development, dump the imported constants in the sub AUTOLOAD and, in the final version, use that output to import the constants explicitly in the importing package.

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