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
This sounds like disk caching which your operating system and / or your hard drive will handle for you automatically (to varying degrees of performance, admittedly).
My advice is, if you don't like the speed of your drive, buy a high speed drive purely for compiling purposes. Less labor on your part and you might have the solution to your compiling woes.
Since this question was originally asked, spinning hard disks have become miserable tortoises when compared to SSDs. They are very close to the originally requested RAM disk in a SKU that you can purchase from Newegg or Amazon.