I purchased these Shatter Proof Bulbs at Home Depot. All I did was measure each side of the hanging part of the bulb and mark it with a Sharpie marker to make sure that the 'ears' would be even. I then took a paper piercing tool to break through the large bulb where each of the smaller bulbs were going to be placed to make the ears. Finally I took a small glue gun and pushed it through the hole made with the paper piercing tool to make it large enough to fit the stem of the small bulb in place adding a little glue to secure it into place.
I have quite a few of these on our Chirstmas tree every year! I loved these bulbs because I thought the larger bulb kinda looked the Space Ship Earth at Epcot!