There are aftermarket clip-on and screw-on wide angle and tele adapters at camera stores and some mega-mart type camera departments. You can rig up an extension tube and lens and gaffer tape and *maybe* it could work, but it would be iffy.
IMO, it is probably better, certainly EASIER, for these types of cameras to apply DOF in post using something like the DOF plug-in from Magic Bullet Looks.
Or, you can build this yourself for free, right on the NLE timeline; all it takes is two identical video track layers, one of them gaussian blurred, and a gradient mask using Add, subtract, Difference or other Blend/compositing modes. You can customize the gradient for each scene to get the effect you want. Magic Bullet just automates the process.
You can model this using stills in Photoshop, it is a popular way to make live action scenes seem to be pictures of ultra-detailed miniatures.
You can also go old school and shoot using much longer camera to subject distance and some ND gel over the lens to try and force a tighter DOF. But this may not work well for cams that use a strictly digital zoom. The post production answer is likely the best bet for this particular camera, IMO
I think you could probably do that, as Mark says, with adapter rings and extension tubes, etc... but there's no way to shrink the size of the front-end hardware. Even if you used one of the smallest DoF adpapters (maybe the little Brevis?), you'll still have a big adapter+prime combo sticking out in front that dwarfs the camera... especially if you attach it to something really tiny like the Flip.
The Magic Bullet suite does indeed work pretty well to give some shallow DoF simulation. It doesn't truly give you a shallow DoF, of course, but does let you knock out some sharp focus on selected areas that can indeed make talent pop a bit.
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I, too, would think this is a situation for post production. If you're going to go to the trouble to rig a DOF adapter to a Flip camera, why not just shoot it on a mini-dv or equivalent camera that would be easier to rig.
The new Panasonic GF1 (the GH1's smaller cousin) is pretty darn small when fitted with their new 20mm f1.7 pancake lens, and is capable of producing very nice 720p60 video & shallow DOF even in low light via its relatively large Micro Four Thirds sensor (_much_ bigger than a 2/3" sensor): http://panasonic.net/avc/lumix/systemcamera/gms/gf1/index.html
Not as tiny as a Flip Mino HD or the new Apple iPod Nano cams, but the GF1 can produce impressive results.