You don't need Dashcode.
Create a directory with the HTML + CSS + JS interactive code with
Raphael.
Add the screen capture with the name default.png.
Add the info.plist file, config the size of the widget and the neme of
the html file.
And rename the directory with the extension .wdgt
This is a valid iBooks Author HTML Widget you can insert in your book.
For more information and example files i have posted the process in my
blog:
http://ibooksauthor.es/widgets-html-con-raphaeljs/
it's in spanish but you have the example files at the end of the post.