I did drill the third progression holes myself.
First I marked the position inside the access to the progression holes(forming a triangle with the two existing holes) with a thin sharp pointed tool. Once I got the mark correctly positioned I marked it stronger with a light hammer blow (which aids in guiding the fine 1mm drill bit) I used a dremel hand drill with a 1mm bit to make the holes. It requires a steady hand and keeping the 90º angle of the drill in relation to the carb bore. Otherwise not much more.
Check out this link, which is where I got the instructions from on how to do it:
http://www.aircooled.net/gnrlsite/re...idarebuild.htm
Good luck!