I'm working on an Aweber follow-up campaign for a client (using confirmed opt-in) and he's complaining that almost 20% of his subscribers don't confirm their subscription.

I have told him that is about a normal percentage that don't confirm. But he's still unhappy. So I'm wondering whether:
a) switch to a single opt-in system (would involve setting up a whole new Aweber account, I think)
b) figure out a way to increase confirmations.

Any ideas or thoughts on either option would be welcome.