Surely the terms of the trial are to be complied with if you are trialing the sytem for the CAA. If you are flying a visual approach if you wish to supplement the approach using the published GPS procedure that is a matter for you - you simply require the permission of ATC to fly the approach visually, which doubtless at Shoreham will readily be given.
I have flown the approach a couple of times without problem and AT are their usual helpful selves albeit the aircraft is on the UK register.