As we know there are two kind of casters: the spontaneous (like Sorcerers) and the ones who prepare the spells after waking up (like Wizards). I always found a little too rigid the system of the Wizard: it is far too easy being with an array of Fireballs when you actually needed Wind Wall. This Alternate Rule tries to find a compromise without making the Wizard exactly the same of the spontaneous caster changing a little the rule that allows you to fill in an empty mind slot in 15 minutes.