The problem I see is the neutral. A 2 wire with ground cable usually has an uninsulated EGC that can't be used as the neutral (plus it will usually be smaller than the ungrounded conductors) and there is no provision to run a neutral outside of the cable or raceway.
If, by some strange reason, they did run a 3 wire (red, black white) cable with all conductors insulated he might be able to establish his EGC with a separate wire.
As for just grabbing the grounding electrode conductor at the well point, You might be able to make a case for it.
250.130 Equipment Grounding Conductor Connections.
Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in 250.130(A) or (B).
(A) For Grounded Systems. The connection shall be made by bonding the equipment grounding conductor to the grounded service conductor and the grounding electrode conductor.
