I made it work without APSL - AlchSpeedBuff with a timer of 15 seconds, and AlchFortifyCarryWeight with a timer of 16 seconds. When the carry weight wears off, the speed is re-calculated and returns to normal. Having them both at 15 doesn't work, but that one extra second on carry weight is the work-around.
Here's the update to test - http://www.mediafire.com/?m7t3yxj7s07ol10
Once the CK is out, the way to do it will probably be to create a script effect that increases, then decreases carryweight in the scripteffectstartblock, then repeats that in the scripteffectfinishblock, with that effect also having a 1 second greater duration than the speed boost effect. It's a minor detail, but that would prevent you from having a higher carryweight for the duration of the spell.