Is it about the rules, or the promotion? To my mind, only people who have already ridden, or at least entered, an event really know about the rules. The important people, if you are trying to expand popularity, are those who haven't done that.
Among club/keen cyclists, Audax may have an image problem. Among those who have never done an organised ride of any description, it's unlikely that there is enough awareness for image to be an issue.
Thus, the Stevenage events (start and end of summertime), which have already been mentioned, seem to have no problem attracting riders of all types, at least at distances up to 100km. You have to be a bit more experienced to contemplate 200km - that's something to do as a further target later on, if you are a new rider.
So what's wrong with promoting a "challenge ride" or similar, open to all who want to give it a go, with distances of 50km, 100km and 200km, for example. OK so 50km is a bit short for a "long-distance cycling association", but the Football League has no problem with starting kids on rather small pitches. The point is to get them to move on to "full size" later. If they began on it, they'd give up and go home.
So forget the few club riders who have an image problem with Audax, and promote to the many in the public who are looking for E2Es, C2Cs, charity rides and other organised events. Tell them that you'll give them the best route in the area, and pitch it as a way of doing something different, and a bit harder than they have ever done before. When they've got the bug, and only then, point out that there's a whole vista of challenge up to and including LEL.
They should get a decent welcome. I've never noticed anyone being ostracised by the rest of the riders in an event, whatever he or she wore or rode.