Knoxx (now part of Blackhawk) have launched a thumbhole variant of their recoil dampening Talon (shotgun) and Axiom (rifle) stocks.
The Talon is available for the Remington 870, Mossberg 500 and Winchester 1300. The Axiom is available for the Remington 700, Howa 1500 and Weatherby Vanguard.
Murdoc has more info about the Talon and Axiom over at GunPundit.