I bet there are some 300s with a 50km short-cut available. Of course you couldn't ride all the way round with the same folk, but otherwise this fits your criteria. You would get company on most of the route - if you're fast, set off a bit late, et vice versa.
If I found you such a ride, would you do it? Serious question. Because this sort of underpins the whole justification of audax rides.
At the risk of veering off topic, if it suited me to adapt the route such as you suggest I wouldn't be bothered about missing out on the points.
I have done this on various occasions this year, in most cases riding the last quarter of the route first or something like that just to fit in with where I live - I still ride most of the route with company, and still ride most of the official route, however that way I don't have to drive to the start.
However I have always paid and entered the event as if I meant to ride properly. This is out of respect for the organiser and the fact that I may benefit from laid on controls.
I disagree that the point underpins the whole justification of audax rides. To me, AUK is a body that organises enjoyable bike rides with like-minded company. Whether my card is validated or I am awarded points makes no odds to me. It just suits me to do it that way.