Configue Outlook (2003, 2007, 2010) to automatically accept .ics meeting requests sent via email

Our hosted software sends vCalendar ics files via email to sync with users calendars in Gmail and Outlook. We need the client software to automatically accept the requests and add to the local calendar without prompting the user. Works fine in Gmail, but we've not been able to do this with Outlook. I'm not sure if it is a configuration issue, permission issue, problem with the ics files or whether we need to use a script/rule as described below here ([login to view URL]). We're looking for the simplest solution that requires as little modification to the client's computers as possible (they are not technical and there are lots of them). Please only respond to this project if you have worked on a similar issue before and already are aware of a solution. Thanks!