The best and probably cheapest option is to glue a nut with the right threading to the bottom of the camera. It'll take up little space and won't be in the way for normal use, but will provide a stable anchor point for a tripod.
An open case or cradle could work, but wouldn't be much of a stable base if it isn't exactly right for your camera, thus beating the point of using a tripod in the first place. Another option would be to use some sort of velcro or elastic straps to hold the camera in its place in a open case or cradle or on a mounting plate, but judging from the picture you posted, the layout of the camera might make this hard. As the straps will either be over the controls, screen or flash.
Ofcourse you could buy a quickrelease-plate and mod that so it can be clamped/strapped to your cam, but for the money you'll spend on that you can probably buy another camera that already has a tripod mount.
So imho a simple nut and some crazyglue (or other sticky stuff) will be your best bet.
