You don't need 192.168.0.0.0.0.0.1. 40 bits covers the world easily, like 1.2.3.4.5. This doesn't mean the field has to be only 40 bits, could be 128 and you don't write the trailing 0s. Of course this means no SLAAC.

But I don't get why the other commenter was proposing putting the 0s at the beginning instead of the end. Shouldn't the new address space be under the existing subnets?