Just about the only thing you can do to speed up the skill switching process is to right click on the skill you'd like to change. By doing this you'll jump directly to the skill selection for that key, bypassing one page of the menus you'd normally click through.

This is the only way to speed up the process of changing skills. There is no other way to automate or hotkey skill selection in Diablo 3. It must be done through this menu.

Any 'out of the box solution' would require, at a minimum, the use of some form of third party macro or automation software, a clear violation of Diablo III's Terms of Use. While such violations are not always detectable or acted on, the possibility of action against your account and revocation of your license to play would give me extreme pause in considering any other solution.

Since bosses and mobs are easily accessible and deaths are of little consequence (in terms of cost to you, including the time required to get to where you were at the time of the death) in Diablo 3, a practice dummy would not have made much sense. It's much easier to just try out different skill combos on actual monsters and bosses.

So the answer is no, there is no such thing in Diablo 3.