Pyro,
If and when you start training and find yourself at a controlled airport all you need do is say "require full length" or "require backtrack".
Don't request it if you really require it, particularly in performance-limiting situations. "Request" gives ATC discretion whereas "require" does not. Having said that, I don't know of anyone in ATC that wouldn't grant your request (with the exception of location-specific procedures, if there are any).
Your instructor should explain all this to you when the time comes.