Your sight is an Impact Archery sight and I have the same one. You should sell that sight in the classifieds section and then purchase the impact archery sight that has the five pins.
http://www.impactarchery.com/hammerhd5.html
You could also purchase the pins from Impact Archery and string the extra fiber optics into the area where there are fibers optics shown in your picture. It will work, there is plenty of room and you will no sacrifice very much brightness.
Best of Luck!