Unfortunately no, you can’t implement hover effects using inline CSS.
A (poor) work-around for this problem is to have your controls render style blocks when they are rendered. For example, your control could render as:
<style type="text/css">
.custom-class { background-color:green; }
.custom-class:hover { background-color:Red; }
</style>
<a href="#" class="custom-class">Coding Horror</a>
If you could force your users to drop a “style control” at the top of their pages you could render all your custom classes there instead of rendering them next to each control, which would be a very, very bad thing (browsers will restart rendering every time they come across a style block, having a lot of style blocks scattered around your page will cause slow rendering).
Unfortunately there’s no elegant solution to this problem.