In my previous post I had only been using Expression Blend and wasn't able to figure out how to get it to generate content for WPF/E. It turns out that only Expression Design can export WPF/E compatible content (thanks ADO Guy).
If you download and install Expression Design, you can create vector-based elements to include in your WPF/E-based web pages. Expression Design is very similar to Adobe Illustrator. Once you've completed your design, click on File>Export>XAML. This will prompt you for a filename then it brings up a XAML Export window like the one on the right. If you select the Document Format dropdown you can select the WPF/E format. I've tried a couple simple tests that displayed correctly in WPF/E Pad.
This is a good step and may be all we need, however I was expecting this same type of functionality with all the Expression tools. Is that coming?