Data::Sorting allows you to pass in a subroutine reference that is responsible for extracting the value to sort on:

  sort_arrayref( $data, -compare=>'numeric', sub { substr (shift)->[0]
+, 2 }, 3 )
[download]

There's also a (poorly-documented) interface to let you specify this in data rather than code:

  sort_arrayref( $data, -compare=>'numeric', -extract=>'compound', 
                 [ index => 0, substr => 2 ], [ index => 3 ] )
[download]