Due to the design of your T-case they can't be modified for a "twin stick" design to allow front axle only. The best choice is to get a hub conversion for the rear axle. You would have the option for lockouts, just like the front axle. This would be the easiest way to lock and unlock them, but not the strongest. Drive flanges would be the strongest but you would have to remove them and reinstall them each time. You could always change out the T-case for an aftermarket one like a Atlas or similar one, they would offer the front axle only mode. Not 100% sure but on the ford style NP208s most people just shift the T-case into neutral to flat tow with out having to remove anything.