I understand what you mean about the email widget. Sitepad has the posibility to start "simple" and also go in the deep.
I look to it in the past and I have the impression that the email client communication is based on a php script between the email widget and the Sitepad software.
Sadly your out of luck, I cannot help you to change the standard behaivior of the email widget.
However I foresee an other posibility that maybe could work for you depending on what you want. I must point to the fact that using the standard widget is relatively simple, addressing an other email address isn't a simple solution.