Dunno if this will work....

If you are not getting off at an intermediate airport ( saying, using the backtrack exception to pass through an airport up to 3 times ) , but must go through it on a Flight with the same Flight Number ( even with a change in gauge )... you might be able to convince 'em that the miles are "as a crow flies" A to C rather than the actual miles point A to B to C.

Assuming they'll grant you the same way they compute FF miles. ( May vary by airline? )

Example, LHR-ORD-SEA is computed as RDM/EQM miles LHR-SEA, even though you may get off and change planes at ORD, and BIS is much higher.