Well, if it's not against the rules, that's actually a pretty good idea. However, if anyone ever changed their mind and joined the WA at a later time, they'd probably get banned from it for cheating. So, it's sort of risky.
I'm going to make a thread on the NationStates forums asking about how specific it is about that. If they approve it, it would resolve the complications with getting a non-WA delegate. I looked it up and they say they use 4 factors to decide if it is a puppet or not. I believe that both nations would have to be logged in from the same computer around the same time for them to see it as a possible 2nd WA nation.
If the person who maintains the WA nation joined the WA, they could just make the puppet nation leave the WA and we could select a new representative.
EDIT: Made a thread asking the mods about it, I'll update when they respond.
EDIT2: And as soon as I make an edit, I get a response
"Unread postby Frisbeeteria » Wed Oct 30, 2013 7:50 pm
It's long been moderation policy that sharing nations is inherently risky. What happens is that it gets difficult to tell exactly who owns the nation, so ALL players who access the nation can get tarred with a bad brush if just one of them breaks rules.
That said, it's not specifically against the rules to share nations. If you and your regionmates want to take the risk, that's your choice. However, I'll tell you in advance that "I wasn't running it when <nasty thing> happened" is not an acceptable excuse. It's a risk, and you simply have to choose to accept it.
As to the specific WA question, the rule is "each player may operate only one WA nation at a time. If one of your shared nation players logs off that nation and starts his own WA a week or a month later, that's not likely to be a problem. If he swaps back and forth between his own WA and the shared WA, that WILL be a problem."
So we can, but we can't be dumb about it and the person maintaining it has to be trustworthy enough not to abuse it.