An answer (see below) to one of the questions right here on Stack Overflow gave me an idea for a great little piece of software that could be in
I had the same idea and did some research. I found the following tools that do what you are looking for:
However, the second one I couldn't manage to get working on 64-bit Windows 7 at all, and it doesn't seem to be maintained at the moment.
The VSuite RAM disk on the other hands works very well. Unfortunately I couldn't measure any significant performance boost compared to the SSD disc in place.