Bouncing Photographer

Okay
So I about a week ago I got a large bouncy exercise ball to replace my chair in front of my computer.
I sit at my computer for sometimes 4 hours at a time without standing up and I've been...bouncing.
Now, I'm not saying I bounce for 4 hours straight or anything- usually I get in the "the zone" or have
to do something really precise and stop bouncing....realize it some time later and get back to bouncing.

My goal is to bounce constantly, so I am never just sitting still.

I am not sure if there is a way to quantify how many calories I am burning while bouncing,
but does anyone know of a way to even get a rough estimate? Maybe a formula or something?

I would appreciate any thoughts!