I tried this once and ended up with the most God-awful gloopy mess in a bottle!
It didn't dissolve properly and I chewed my way across the Lakes!
Consider taking the Gels which are a concentrated version of the powder in an easily manageable squeeze.
Or, if you're seriously concerned, you know where the feed stations are going to be as you'll have a map on site. Jump in the car the day before and put some refueling items at stragetic points (maybe alongside the feed stations as you'll be stopping at these anyhow) .
Tim
ps- what's your girlfrind dong that day? Why not have her in the car with your stuff at or near the feed stations?