On a Blue Pig MK1 you could probably use the threaded fender mounts to attach any normal rear rack to it, since the rear disc caliper is mounted out of the way on the chainstay. The upper rack stays can be attached to the seatstays with p-clamps.
The Blue Pig Mk2 doesn't have any such mounting points, so it's more complicated. You could possibly rig something up with p-clamps or hose clamps around both ends, but the possible weight you could haul will be greatly diminished. You'd probably want to look at a rack that mounts to the axle, such as the ones made by Old Man Mountain. Alternatively, you could get your local framebuilder to braze on some threaded barrels to fit the rack of your choice - it shouldn't be too expensive, but you'll either need to repaint it afterward or deal with some ugliness.
Depending on how much work you want to do in swapping the frame to "adventure" mode versus aggressive mountain biking mode you might look at a rigid fork, such as one from the Salsa Fargo or the Surly Ogre, and hauling front-end loads. Riding long distances loaded and with a 140mm travel suspension fork is in itself not going to be particularly enjoyable.