How can i make an easy "manufacture" in order to have balloons falling at a specific moment of a festival?

Question

You can check the following addresses in order to have an idea of what i really want.
I want a way to have balloons somewhere on the roof, and in a specific moment to pull something (or another way) and let them fall... How could i do such us thing?
Thanks in advance

http://www.d21c.com/BARB/BDAY/BG-CELEBRATION.JPG
http://silicon-valley.siggraph.org/text/MeetingNotes/Sig98/BalloonsBig.JPG
http://www.thealabamabaptist.org/images/siteimages/12/lauren/Final%20celebration%20RGB63005.jpg

Answer 1

Look at www.StumpsProm.com They offer 2 diff rent types of balloon bags. You can also go to any Party City in your area. They also offer balloon bags. All of these bags must be manually released.