Tee, sorry I forgot to address your actual question after my little rant!
In short
Outlook can only have one default calendar, I do not believe there is a way for you to have a meeting that you accept go into two calendars automatically.
You could manually copy them over, say at the end of each day
Right-click your source calendar and select advanced find
Do not enter any search critiria, just click search
use CTRL+A to select all items
Drag all items from the search window to your server-based calendar.