For most of my photoshoots, it is just myself and the model working together, without anyone else present. I am looking to do some more commercial work, and have noticed that places like istockphoto require that a witness sign the release also. I know there are other photographers who do solo shoots with models and was wondering how you handle a release that needs a witness signature.
Thanks.

make a quick 30 second video of the model saying she signed the release.

Not sure if it would work for the company stated for that is a hurdle of red tape which may not be based totally on logic.

Or a quick few shots of her holding her ID and the signed document.

You might just ask the company or companies you wish to deal with.

I e-mail the models the release & require they show up with it notarized when possible.  If not, I have my assistant & the model's escort (if present) or a stranger (store clerk, mailman, anyone) witness it & take pics.  I always photograph the model with her face, the release, and her ID clearly visible if it's not notarized.
You're asking for trouble if you use non-witnessed releases.
The poor bastard whose life that worthless b***h Cameron Diaz ruined went to JAIL over not having a witness for her signature on his release.