If I read your question correctly, you have something like this?

use strict;

my @universe = sort complex_sort (1001 ... 5000);

my @random_offsets = (503,1083,260,5,101);


my @subset = @universe[@random_offsets];
print "unsorted subset:            @subset\n";

# Want subset in same complex_sort order as @universe
# Can do a quick sort on the index, as @universe
# is already in the order we want!
# Option 1:
@subset = @universe[sort( {$a <=> $b} @random_offsets)];
print "sorted subset: indicies:    @subset\n";

# But if unable to determine the universe indicies
# in advance, we might have to sort the subset once
# Option 2:
@subset = sort complex_sort @subset;
print "sorted subset: complex_sort @subset\n";

sub complex_sort {
  return $b <=> $a;
}
[download]

Regards

Jeff