You just need to create an expert mode FlexRAID config instead of cruise control.
With expert mode, you can set your 7MC to record directly to the OS drive path instead of using the storage pool and then point your storage pool to the same folder. However, you couldn't use hard drive space past the 1 HD except to manually move them to another drive in the pool (and define the DVR HD as restricted so the storage pool doesn't add files to it). I would discourage this route in any setup, though. You do not want your Live TV Buffer on a snapshot parity. It will basically make your parity worthless because the buffer is constantly editing and deleting which is corrupting your snapshot.
You'd be surprised how quickly the live buffer can corrupt data. I accidentally deleted about 800GB of recordings due to moving the DVR drive to a new HTPC and pointing 7MC to the record folder but not telling the DVR to use the entire drive (it defaults to 200GB or so). So when the next recording came up, 7MC saw that it was over it's defined allowed space and deleted all the oldest recordings to make room. In the meantime, live TV was running for about 2 hours before I noticed this. When I went to use a deleted file recovery software, I could only get about 200GB of data back. That's how quickly the live TV buffer wrote all over the drive and corrupted the deleted files. This exact same scenario would play out on your snapshot parity if a drive failed and you were watching live TV before performing a snapshot update.
Only realtime RAID would work in what you are seeking, and that won't work because it won't be fast enough in writing throughput to do multiple recordings. The only setup that would be capable is hardware RAID5/6, and it isn't worth the investment.
Instead, you should look to set your DVR/Live Buffer on a drive/folder outside of your snapshot parity. If you want to parity backup your recordings, then you should use a script/program to move the files from the Recorded TV folder to your storage pool with snapshot parity. Another option is in expert mode, you can define folders for the snapshot parity to ignore (so you could set the live buffer folder to be skipped) and it won't corrupt your parity. I haven't been able to figure out how to get it to work.