You need to be very careful of not only the projector, but to be sure you have a mount which easily allows it to be repositioned. You will need to watch the image size, and the projector will likely need to be zoomed/refocused at the proper size when this is done.

As someone who does this for a living, this is not the type of task I would just hand off to someone who isn't experienced with front projection, as it will be a lot of work to find projectors which can handle pointing up/down and to handle the zoom requirements.

You haven't mentioned a budget, which hopefully means you haven't set one, and are prepared to address your unique situation appropriately.

I might go with a mirror bounce that can be put in front of a projector to bounce it downwards instead of repositioning the projector every time I was going to change the setup.

.6m or less is only about 2 feet. What type of projection size are you expecting from this distance?

I think, realistically, you are getting into a situation which will be extremely difficult for an end user to utilize, and the initial setup and calculations are really going to be miserable.

I would offer up that perhaps the Conen table from Epson may be a good solution as it is a interactive whiteboard/table which is motorized and the projector and screen move together to maintain focus and operation.

http://www.epson.com/cgi-bin/Store/jsp/Landing/brightlink-pro-collaborative-whiteboarding-solution.do?UseCookie=yes

Towards the bottom of the page is the Conen.

Here's their website:
http://www.conenmounts.com/index.php?id=5