Have you read the Q&As? (Follow link at top of page.)
It's not clear to me what sort of case you're trying to present.
Do you have alternative evidence of ability in NVR? Some schools, for example, do CATs, which include NVR.
Failing that, if you're lucky, you might find an educational psychologist willing to test just NVR:
http://www.elevenplusexams.co.uk/11plus ... ers.php#b3
Time is very short, however.
Are you arguing that your son underperformed because of his stomach problem, and, if so, what evidence are you putting forward?
What arguments are you putting forward against oversubscription? You mention the bus journey to the allocated school, but is the journey to the GS much easier, and is your GP likely to support this?