I basically asking the same thing. I want my OS on the SSD, and data, etc. on a physical separate hard drive, and still be able to use RST. Looks like I'll be calling Intel about this...
I have done this but my method is a little backwards.
I first had a HDD OS on my Z68.
Then I attached 2 x 1TB HDDs and a 120GB SSD.
I made a RAID1 using the 2 x 1TB HDDs.
Then I SRT accelerated the volume using my 120GB SSD.
When I selected my 120GB SSD as the cache disk, it split the SSD into two parts and I noticed I could use the remaining space of the SSD as a normal windows partition.
Therefore, I just rebooted and used the remaining SSD space to install Windows 7 64-bit and starting using that disk instead of my original HDD OS.