filter events by group (relates to event, og and og_events)

Hi,

I am building a site for a multi-group organisation, each group is in a different geographic area (we have 45+ locations) The event link on the main navigation menu shows all the events, it would be great if the user could then filter the events by selecting one or more og groups to which the event is targeted (the audience option in the create event). Currently it is non-intuitive that some aspects can be filtered from here but to see targeted events they must go into each of the groups (many of them are geographically close) so the user must browse to lots of different og groups and view the og event calendar.

In essence I am asking for a multi-select filter box in the event module to filter by audience.

thanks for your time

Richard