I tried it for the Sistership Mod 2.0. I think it is not possible, but it is what I think. Perhaps someone finds a way to add some new voices.
Resynchronizing with RealitySorry, You're Not a Winner
18th April 2006
New voices are possible, no doubt about it, however, new captains aren't yet confirmed if they are possible or not. I'm sure someone will find a way in the end, but you'll have to be patient about it.