Software that automatically move unused files to external hard drive ?

Hi

I have a macbook with 500 go. I wish i could have a 2 TB hard drive inside but i t doesn't exist, and i don't want a dual hard drive.

I need an external hard drive to copy all the sound libraries that i use for work. But then i won't be able to work without carrying the external hard drive everywhere, so it's kind of a bummer. Especially knowing most of these files are hardly ever used, but i need them at my disposal just in case.

I was wondering : is there any software that automatically copies files that were unused in the last 30 days on the external HD, and put the most used ones in the internal HD ?
This way i can work on my current project without the External HD.

thx