Seem to remember that Virgin tried something like this after 9/11 when they decided that the 747 Classics would operate soley from MAN, but the crews would still be LHR based. The crews wanted a mileage allowance, but the company issued them all with a Virgin trains railcard instead. The crews were'nt too impressed, so they started to use the trains to get to MAN leaving on the latest train that would get them to report on time.
The result: they got their mileage allowance!