It is my understanding that yes, you can.
But, I don't think you should.
Taking 20gb or so away to cache a hard drive reduces your space on the os drive.
If the data on the hard drive is so frequently used, it oould be better resident on a larger ssd in the first place. Particularly if it gets many writes, since writes have to be done to the underlying hard drive anyway.
It is possible that some usage patterns might benefit. Say, for example that you have 20 10gb games on your hard drive, and that you will play one or two exclusively for a couple of weeks, and then switch to another set. That pattern would allow faster reading from the ssd cache than from the underlying hard drive.
You could try setting up two ssd partitions before loading windows. Use the second partition as a smart cache, and see if you like it. If it does not work out, you can recombine the partition beck into the "C" partition later.