Clearly a job for a DIY, surely?
I have a route that passes near (Chatteris->Ely->Brandon is one section of it) Cambridge that could be modified to suit your needs.
Do some research on DIYs, including some searches of YACF, and see if that kind of ride will suit.
TBH, deliberately entering and then DNS'ing a ride is probably not "in the true spirit" of Audax, and has a similar taste in the mouth to riding the route on the day of an event, without actually entering it.
There are quite a few DIY regulars in East Anglia - we'd be happy to pass on any pearls of wisdom we may have - and may well ride out with you if we can
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