I followed ChrisF here and write a simple demo.
...open your project in Expression Blend, select the button and then right click and
I realize this is an old thread, but I found it when I was trying to do the same thing and didn't find any great solutions. I thought I'd post what I came up with in case it helps anybody else.
What I wanted was flat buttons that used the normal chrome when moused over. The best way I could find to do this was to cheat and use two ContentPresenters inside a Grid with two rows. One content presenter is inside the normal ButtonChrome and one is inside a Border. Only one grid row is shown at a time and the setter in the IsMouseOver trigger determines which one is shown.