It seems unlikely, given your UK licence plate, that you can get the Spanish ITV to be recognised to apply to your vehicle.
You probably know that for the MOT testing to be valid the testing station has to log on to some website or other (VOSA/DVLA??) for a minimum length of time that is related to the complexity of the vehicle test process; some test stations have lost their testing status on this account alone.

On another thread you have discounted using a van to get the bike back to the UK, so that appears to leave the alternative of riding the bike back here very carefully indeed i.e. as you say, you may not be covered by your insurance if involved in a claim from any party (because of the lack of a valid MOT certificate, but this may not be the case - it depends on the insurance company, their insurance assessor and your full circumstances). It is very unlikely that you will be asked to show UK specific documents (MOT, tax disc) unless you are involved in an accident or when near the channel ports, at which point the French authorities are reputed to be much more aware of the UK legal requirements for motor vehicles.
Ferry, Santander >> UK worth considering?
On arrival in UK, go straight to a pre-booked MOT test which happens to be near to where you are heading in any case (or get a mate to pick you up with his van, or get a transport outfit to take the bike to your address).

__________________
Dave