The device only supports one calendar.

One thing you might look at is using a Google Calendar and one of the gmail sync tools (Like oggsync) with some sync rules. You could not sync directly with Exchange for calendar and use the oggsync client on your PCs and mobile device to sync/merge a local copy down to the phone.

I believe you can also just sync some of the details from your personal calendar (e.g. free/busy data) up to your Outlook calendar with OggSync.