I've generated a new SSL certificate, marked it to have an exportable private key and imported it to the ADLDS instance's personal key store. I've also given "Network Service" access to the certificate file in MachineKeys.
When I try connecting to the ADLDS ssl endpoint, and have process monitor up, I can see that an entirely different file is attempted read from the MachineKeys folder. That is, the second part of the "GUID_GUID" filename is the same as that of the file created when I imported the new certificate, but the first part isn't.