I don't have experience with nitrogen mixes, other than I understand that nitrogen doesn't absorb the way CO2 does. This is why pubs that push their beer long distances from the keg to the tap, use nitrogen to push instead of CO2. They have to use higher pressure for long distances (we're talking the length of the pub) and higher CO2 would get absorbed and over carb the beer.
If you have the time, I'd prime them with corn sugar. If not, and you don't want to waste precious nitro on forcing (shaking). I'd say do the passive force carb. Hook em up at serving pressure and let em sit for 7-10 days.