The use of the Continious (+1/2 ?) and Uncontrolled (+1/2) advantages should do the trick. Generally, the utility and defensive spells are quite cheap for a fantasy game so you can afford a higher active point total for spells based on these effects. The advantage is that you can freely switch slots once these powers have gotten rolling - provided you've allocated some END to running them.
In the end, it boils down to how much END you allocate to each spell. I use a variant of the Reduced END advantage called Duration for spells: Pay END every Turn (+1/2), each step down the time chart is an additional +1/4. Basically, you wind up paying more than the 0 END advantage but I generally disallow that for spells anyway
!DrFURIOUS!