Nah...That's gonna work unfortunately. The TM Breacher's gas source in in the pistol grip. That series of TM shotguns uses a gas reservoir independently of TM's 30 round shotgun shell magazine.
If anything look at the APS gas powered shotgun, its a gas shell powered, shell ejecting design. Maybe there's a way to get that to work with a masterkey kit. There have been multiple iterations of the APS system, if the masterkey is just a fantasy, I'd hold out. I wouldn't be surprised if APS or another company ends up offering a masterkey type under barrel attachment/kit using this system in the future.