NP1112 - the whole carbo-loading, pre-race meal thing definitely takes practice. Over the years I have tried various strategies during training and this is kind of the one that now works for me.
You're right - it's really trying to top off stores by consuming 600-700g of carbs each day for the two days prior to the race, and then getting in that last "top off" prior to the race. The Gu 15 minutes prior lets it settle before I start running and is like 100 calories in the bank before the race even starts. I then take a Gu around 4mi, 10mi, 16mi, 20mi, and I'll carry an extra one for "emergency purposes" beyond that if I need it. I also try to get 2-3 gulps of Gatorade out of the cups every 2-3 miles.
This was the first marathon I was able to comfortably consume that amount of calories (which I rehearsed in training), and probably no coincidence, the first marathon I finished without hitting any wall.
I initially tried eating most of the calories 3-4 hours prior to a long workout, but I always felt "heavy" doing that when I started running. For some reason, spacing it out in little manageable quantities works better for me - as does getting about 200 calories from the Gatorade alone.
To each his/her own, and I always recommend trying a variety of strategies until you find one you are comfortable with and then stick with it. For me, my thinking is, if you can handle that amount of calories, then why wouldn't you take it? It's like energy in the bank. :)