Unfortunately, I never did find a satisfactory solution. On a Mac, you can generally use an fmp:// URL to call a script to save the data, but the URL size limit in Windows makes that less reliable for long-form data (like a textarea).
If CWP is an option, you can also just have the webviewer post to CWP and integrate the data that way. But if you're doing it 100% locally, then it's still a problem.
I started this solution on a Mac and everything worked great. Then I found out about the limitations on PC. Oh well.
You are right though. My next move is to use CWP to populate the data. Thanks for the input!
If you are willing to use a plugin:
The Monkeybread Software plugin has a function for this. See: www.mbsplugins.eu
One of the functions is
MBS( "WebView.GetHTMLText"; WebViewerRef )
Ofcourse you have to parse the content and separate the included js code from the HTML.
Only prob I have: TinyMCE has its own formats for html - and I do not know how to get real html from it. Any ideas?