Here is my suggestion:
http://www.youtube.com/watch?v=U5tHtntT9gU
The constant speed stick is running at 12RPM, which will give you a pound every 5 seconds.
To achieve this I recommend using a CIM (
http://www.andymark.com/product-p/am-0255.htm) running through a high reduction planetary gearbox (
http://banebots.com/pc/P80K-S4/P80K-4444-0005). You can put a standard #35 chain 12 tooth sprocket (
http://www.andymark.com/product-p/am-0166.htm) on the output of the gearbox, and attach a 22 tooth sprocket to the stick (
http://www.andymark.com/product-p/am-0216.htm), then run #35 chain between them.
I have more ideas about the construction of it, and the exact configuration of the drive system (shafts, keys and bearings), if you would like extra details like that just ask.
PS After typing that I realized that you may or may not understand any of the words I wrote, feel free to ask for clarification and I will explain our CD jargon.