Outlook: Favourite Calendars

I often use the Outlook feature of looking at other peoples calendars.
There is a MRU list for the calendars, however, there are certain ones that I use more often.
This sounds a bit stupid, as if I used them most often, they would be in the MRU list!
However, sometimes I do bump them off the end even when I would like to keep them on.
What I am trying to achieve is to add a drop down to the toolbar with my favourite calendars in.

Has anyone already done this?
Has anyone got a spark of an idea on how to do it?