I just had a thought - and so far this seems to work ok.
Create another static page to hold your form and save it in the BE folder.
Now create a textbox widget, and use an <iframe> tag to add the form to your text box.
<p><iframe id="datamain" src="http://www.yourdomain.com/pathtoyourform.htm" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" width="100%" height="400"></iframe></p>
Now when you submit the form within the textbox widget, it doesn't interfere with the .net form tag or mess with any BE stuff.
However, if you're creating a "subscribe" or "optin" form for an autoresponder like me, you'll also need to make some custom "thank you" and "error" pages for when the form is submitted. Just create 2 more static pages and put those in the BE folder too.
Then when the form is submitted, only the portion within the <iframe> tag will be really be submitted, and that <iframe> will refresh without affecting the rest of the page.
Hope this helps save some frustration for others...