Well, sort of....

Chiltern are now offering free weekend travel over its whole network
if you buy a season ticket costing more than £150 a month or £1500 a
year. A Z1-6 Travelcard is more than this. Marylebone is the only
station at which this can be issued on Oyster.

See http://www.chilternrailways.co.uk/ti.../new-customers