[HELP] pagination w habtm association and authorization plugin...

I am using the proven authorization plugin to defines roles for users,
so I can get all groups where a user is 'member'

@groups = current_user.group_memberships

I have an habtm association between groups and events

class Group < ActiveRecord::Base
has_and_belongs_to_many :events
..
class Event < ActiveRecord::Base
  has_and_belongs_to_many :groups

I am trying to list and paginate (with the will_paginate plugin) all
events in all groups a user belongs to...

I thought initially to build an array of ids from @groups and
paginate :
    @events = Event.paginate :page => params[:page], :conditions =>
["group_id IN(?)", group_ids]

but group_id is not a key in the events table....

any hint ? thanks