Here's a tip that has helped me learn my new layout of choice while remaining proficient in QWERTY.
Change your computer's password to the English alphabet (A through Z) followed by your normal password.
If you're on Windows, when you initially log in you'll need to type out the alphabet in QWERTY. When you unlock your computer from sleep mode you'll need to type out the alphabet in your new layout. This works best on laptops because they are generally turned off and on more frequently than desktop computers. Also, be sure to enable the setting that prompts for a password upon waking from sleep or hibernation.