While it doesn't go all the way around the lake, there is a very nice path that runs along the western and southern end of Bay Lake and goes between GF and Poly. It's not a heavily traveled walkway, so you should be able to jog there without problems.
The quickest way to get there, is to take the monorail around to it (get off at Poly or GF). You could also walk over to the boat docks at MK and boat to either resort. There is no way to walk over there, as there is a thin section of the lake in the way.
There is of course the pathway from CR to MK, but I would assume that's just too crowded with MK guests to make running feasible.