iSCSI Differencing disks by snapshot?

I have a somewhat stupid idea I wanted to throw out there.
Since ZFS is supposed to be copy-on-write, could I take a snapshot of a dataset that contains a single file-extent, and then use cloned snapshots as a file-extent target?

Instinct says no, it would effectively be the same as dd'ing the file extent anyway, but I thought to ask just in case it could be a thing.