Eventually got my reply from the CAA around the solo x country. Looks like it will need to be supervised:
Supervision implies some level of responsibility for your actions and the authority to determine whether you fly or not! I suggest you ask them how this is legally possible! If you are a qualified and current pilot, as PIC it is you that is subject to the law not the supervisor, you cannot delegate such responsibility neither can anyone assume responsibility on your behalf. You should try asking the CAA for an Exemption from your responsibilities in order to meet their requirements and see what happens.