I would suggest that you increase the account creation fee by a week or two worth of RCs for minimum human function - which won't make much cost difference there - and transfer them to the new account on signup, in much the same way Steem was under the previous system.
That wouldn't enable spammers as much as a full bump to the account's maximum and recharge rate, but would allow it to transact for its first week or two while it earned a few Steem to get it moving on its own.