Though there is one solution I can think of. Which is to require a transaction fee on all coins sent that are not a day old. So if you try to send coins that are not a day old (i.e. don't have 576 confirmations), you need to pay 0.1 ltc fee. What do people think about that?
It's a cat and mouse game. Would not the spammer just use coins that are two days old in that case?
He would have to wait 2 days to be able to spam again after he exhausted his funds.