Looking for a way to improve inbox deliverability for one time emails

I am currently using Amazon SES with very poor deliverability (About 6% on a 50k list). I only send an email to the list once and do not send it again. I have heard of using rotating IPs and clean ISPs but I read that a reputation has to be built up. Is there a way to temporarily get ahold of a good one for one email that would improve the deliverability?