How to set shared mailbox as default for sending mails

I've two machines, one got office 2010 and another office 2007.

In both i've configured my office mails, along with the a shared mailbox. Whenever I'm sending an email by default it is taking up my official mailbox instead of shared mailbox.

If i've to send using it from the shared mailbox, i've to select it from "From" in office 2010 and "Accounts" of office 2007 below the send button and select the shared mailbox.

Is there any way where i can setup the shared mailbox for sending mails by default instead of selecting it everytime ??

Thanks & Regards, SantoshBarad Ashwatha.