I know that we don't have access to some sort of template on the customer zone level.
Personally, when customizing this page type I usually apply a combination of jquery and css (which sometimes is a pain, but we work with what we have).
Here is my usual process:
1. Have css to hide the login form section (if applicable). Use jquery if needed.
2. Create a new element (or elements) that will house your form and place in a script component.
3. Onload/onready of the page, use jquery's clone() call to replicate just the elements that you need (for me: loginName and password input boxes).
4. Before appending the cloned elements to your container(s), change their id and name attributes so there is no conflict with the original elements.
5. Before appending the cloned elements, apply onchange and onkeypress events so that the values of the cloned elements are transposed to the hidden original elements (this bit is for submission).
6. Append the cloned elements to your container(s) and apply you should be able to apply css.
Hope that helps. I know it might be a challenge but due to the lack of obvious options this is my usual process.
I hope there is another easier way that I don't know of. In any case, Good luck!
That's a pretty long-winded way of doing this. I'm quite interested to know if there is a better way to achieve this?
It isn't a pretty solution. I am also interested in finding out a better and less coded option to going about this as i indicated at the end of my response. Hopefully progress hops on this thread with something.
If they don't, then I'll keep using the solution I always do haha