Below is a quote that I understand as confirmation that it takes time for the IP to turn white, This probably only applies to IP addresses that have not been associated with evil in the future. Unless the accounts are blacklisted or permanently blocked, this can be a viable strategy to avoid being charged.
Well that's what the evil fee is... the account is essentially banned immediately after being registered. So no, if you register an account and wait - it won't get the fee lowered. The only ways to get a lower fee (or no fee) would be finding a "clean" IP or waiting until your IP's evil decays, both of which seem kind of unpredictable, and
then registering an account but you don't know how big the fee is until you register. A bit of a chicken-egg situation, which probably results in a bunch of throwaway accounts that spammers create to probe for evil fee amount.
The amount of evil associated with an IP decays slowly over time, but the amount of evil associated with an account does not. You must pay or be manually whitelisted to enable posting on one of these "banned" accounts.
The more I think about it the more it looks like a problem for legitimate users who register through e.g. Tor than a real impediment for spammers who can automate it and upon finding a "clean" IP register a large number of accounts through it.