[quote} In a closed, unannounced meeting, they decided they want to keep the current plan.[/quote]
Are they even allowed to have a closed unannounced meeting over planning? And I think you should make a stink over the veto power of the association only at the council meeting. The street belongs to the community and not just the association. The street obviously impacts those who do not live within the association.
Neck down of the street is a common method being adopted often. My old town adopted it but the street is more than wide enough to accomodate it. The street was almost wide enough for two lanes in each direction.
Also contact some well known bike advocacy group like the ones in NY or one here in Portland, they may be able to give you some idea on dealing with this.
Problem with the planners is that they are still very much car-centric and pedestrian/cyclist is only an afterthought. Stay calm and logically work out an argument as to why they need to change their decision. It's hard, but it can be done. You may have to use their bylaws against them things like when are they allowed to have a closed and or unannounced meeting, why is that the association is the only group with the veto power when others in the area use the road, why isn't there a comment period for the change etc.
Take a deep breath think of an argument where you can corner them, or where their action of installing a neck down might lead to increased liability for the city. Other calming techniques are using a small islands in the middle of the intersection, a mini, turn-abouts is the way to think of these. Check this idea with BikePortland group.
wish you luck!!