I say go for it :) . I sit here on the couch while working on the computer and bounce :), no kidding.. (I have this great couch.)I've used a ball in the past also.
In a pinch, the edge of the bed works as well.

In DMr. Wests's Lymphology book (Title= The Golden Seven Plus One), he says that if someone is injured or disabled and unable to use a mini-tramp while standing, they should sit on it instead and use their hands/arms to bounce, or get someone else to bounce them while sitting, if they cannot do it themselves.

So why not on a ball? You'll still be on a resilient surface, not like jumping up and down on an unresilient floor..

Here's another thing you can do:
sit facing forward on a couch or chair.

Imagine or visualize as if you had a small child on your knees (Using *Both* knees), and imagine you are bouncing this child up and down rhythmically *without* striking your heels on the floor (Just the way you might do a 1-yr-old). The balls of your feet should not leave the floor, and the "bounce action" comes from your arches and ankles.. Your heels stay off the floor while bouncing.

Get your knee-bounce going, and you will find that the bounce-action can become self-propagating. Speed the rhythm up to where you want it.

Then lean forward and rest your elbows on your knees while continuing to bounce from the balls of your feet.

This causes your arms to be drawn into the bounce action, also. Rest your bouncing hands lightly against each other, so that you can relax your arms and let 'em go with the rhythm. Don't worry about whether you keep the knees together or whether they start to 'walk' and alternate, just keep it going either way.
It's a blast :).

You can use that if the minitramp causes your feet/legs to cramp or hurts your toes like it did me at one point :). I don't like to wear shoes, and barefoot bouncing used to hurt my toes.

Course, that was before I got this great couch :).

I also do this knee-bounce with a tray across my knees (Elbows on the tray, a little farther apart than my knees. I let my knees 'walk' for this one), which is a little more agressive bounce that acts as a kind of lymphatic pump to my shoulders. Really helps to loosen up my mouse arm :).

Best of Luck,

Ladylove
Spirit of play, brainchild of the mother of invention..