The layout of the Login Form and Register Form is included in one container with the following structure which is hard coded in the page.
<div id="Container">
<div id="LoginForm">...</div>
<div id="Register">...</div>
</div>
Therefore the layout is not controlled by the user. In order to achieve this goal, I sggest:
1)Add 3 classname for the above 3 div and put it in the template css file which the user can customize
2)Add an option to show both form