I have, sort of. I made a vow to run across the map once. I started at the airport, and ran all the way to the islands at the very northern tip of the map. My friend, driving any truck he could find in order to tempt me to get in a car, and fail my vow. He swam across the Alamo Sea with me, and proceeded to gently tap me with cars,when we got to the other side, so that I would fall over. Despite this, I made it across, found some derpy NPC's and took some victory selfies.
Yeah it definitely sounds like a nice break from shooting guns and bazookas all day. I think small mini games you invent always breathes new life to such a versatile game like GTA.Lol, I've never tried it but it sounds funny. Fists only would make it even funnier. I'm actually going to try a foot race out one day lol.