You can skip $skip characters pretty efficiently simply by using /.{$skip}/. There's probably an index somewhere, since the regular expression engine needs it to keep track of /g matches, but I don't know how to directly access it. (It's pos, as tilly noted below.)

Update: wog reminds us that this requires the /s modifier, or a re-write as /(?s:.{$skip})/ to catch newlines as well.