I suppose that the #6 wire might fly since it could be called a grounding electrode conductor. Split bolts are fairly expensive, but then again, with #12 wire costing what it does, if the runs are over about 20 feet, then the bug would cost less than the wire. If this is a viable option, this would also allow additional receptacles to be converted in the future.
The reason I'm asking is that 250.130(C) addresses a receptacle (singular) and not receptacles (plural).
(Sigh) Had there been code enforcement in WV back in the late 70's, this house would have had grounded receptacles to begin with.
[This message has been edited by Tom (edited 10-26-2006).]
Few things are harder to put up with than the annoyance of a good example.