You don't need to put the sub in the other package in order to access that package's variables. Just refer to them explicitly, as you do in the assignment.

$var = 'one';
$mypackage::var = 'two';

sub we_got_the_func {
   print "Other \$var is $mypackage::var\n";
}

we_got_the_func();
__END__
Other $var is 'two'
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