Although not the most ideal solution, this is definately more ideal than hacking the core...
// Move the excerpt box above the WYSIWYG editor
var $excerpt = $('#postexcerpt');
var $wysiwyg = $('#postdivrich');
You'll probably also want to check that you're on the correct page (and that both of those DOM elements exist) before running the above, but it should give you an idea of what to do.