I see a few problems here - first off you would need to be in the lead at the start of the race in order to drop the marbles. Second, you would need to stay in the lead and hence might need someone to reload the marbles about a mile later or so.

Here's a quote from my son (5) after a 5K last Fall where I pushed him and his sister in a jogging stroller while I ran alongside my 10 year old.

"Hey mom, Shelley and I beat dad!"

Next time, I'm dragging the jogging stroller behind me.

also, we were all wearing costumes (my son and I were spiderman and my daughter was bat-girl) and the race director made a point to come over to me after the race and tell me that unfortunately I was the third super-hero to finish. Once again, need to drag the stroller behind me.