The answer to your question is likely going to require quite a bit more information, as advice on how to improve a workflow largely requires more knowledge about the current workflow, and what’s wrong with it. Hopefully, the following can get you started in solving your problem.

First, ask yourself a few questions.

What is it that’s leading you to believe that EB is too technical for your designer? Is s/he genuinely trying to learn it, but is somehow getting confused? Is s/he resistant to learning it because it’s not Photoshop/Dreamweaver? Is s/he actually getting lost on the coding part, and not EB itself? Can s/he handle some coding in a different editor (SublimeText, Notepad++, vanilla Notepad)? It may not be EB that’s the problem, or even the code, but the combination of both, if s/he is new to both EB and coding.

Additionally, what, exactly, is wrong with your current workflow? What are the problems you’re running into, and how would teaching your designer Expression Blend fix these problems?

Then, ask yourself what, exactly, you want your designer (and your developer) to do.

Should the designer be responsible for actually writing out the styling and animation, or should that be left to the developer? How much styling/animation should the designer do before “escalating” it to the developer? What are the developer’s responsibilities (the ones given solely to the developer)?

Finally, ask yourself if there’s really anything to gain from having the designer learn Expression Blend, learn to code, or if there’s a better way.

Is your developer experienced with front-end development? Is your designer? If your designer is not experienced, and your developer is, then why move the responsibilities? Are you actually gaining enough from that to compensate for the extra time required for the designer to learn and overcome the nuances that are involved in front-end coding and produce good code? HTML, CSS, and JavaScript are a lot more powerful than meets the eye, and all three tend to give you enough rope that it makes it very easy to hang yourself. Will the gains of having the designer write the front-end code compensate for the longer development time and more difficult to maintain code that will likely be a result?

If you do feel that the benefits outweigh the costs, then I recommend taking a step back and starting your designer out with learning to code. As I said, a new coder can easily write themselves into a corner with the front-end languages. Literally, start them out in a more basic text editor, with little more than syntax highlighting (Notepad++ might be a good starting place). That way, they need only focus on the code and not the code plus the editor. Once s/he is comfortable with and reasonably proficient at coding, then introduce Expression Blend. That way s/he isn’t “drinking from the firehose” and getting overwhelmed.

The “learning to code” process can be broken down further, too, if necessary. Start him/her out with just some HTML, so s/he can see how the elements themselves lend to the design. Then add the basic CSS on top of it, and build up the CSS. After a while, you can then start to phase the JavaScript over, as well, the same way you did the CSS.

If your designer is already experienced in coding (and I mean actual coding, not using Dreamweaver’s WYSIWYG editor), what advantages are gained by making him/her use EB?

In either situation, are you looking to use EB’s WYSIWYG tools to do this stuff? If so, again ask “why?”. What is your designer using now? Would teaching your designer to code (or letting him/her code if s/he already knows how), if you don’t want your developers doing the styling and animations, be a better option?