While direct "unicast over multicast addresses" isn't possible as Ron has pointed out, it should be possible to tunnel unicast over a multicast network or, in another perspective, create an unicast-enabled overlay network on a purely multicast one.

You "just" need to find a tunneling protocol that supports multicast destinations, regardless of (unicast) source addresses (which you could - possibly - NAT statically). I'm not at all sure if that even exists but with sufficient effort, it could be created.