The only professional review for the Y500 is the notebookcheck article and the guy states the msata is for cache only, but you are right there may be work arounds for the tech savvy.
I have the real answer to the question after reading NBR forums on this very issue. It is possible and it's not that hard. This software [extend-partition.com]
is the answer. You use the "One key migrate OS to SSD" feature to clone your hard drive to the mSATA drive and there should be no problems. You then set your boot order in the Bios to the mSATA and you're done.
The problem lies in how Lenovo decided to go with how the Windows License Key is stored and how the bios boots Windows in the first place. I'll skip over the technical explanation, but basically if you want to use the Windows License that came with the machine, the computer expects the hard drive to be partitioned in a very specific way. If it is not partitioned in that way, the bios won't validate the copy of Windows installed on the drive.
This is awesome. That means I can order a 200GB+ mSATA and use it a primary drive. Thus, keeping the 1TB drive it came with for file storage and what not.