Yep, I just posted almost exactly this on the blog.
If I got my redirect working, it killed all Wordpress's pretty url rewriting. Hopefully that was just an issue in my specific case though.
If the redirect rules don't work, there's lots of Wordpress redirect plug-ins though. I've used some in the past for when a post is edited and the slug is changed between initial social media burst and finalizing. Just a redirect from the old URL slug to the new one.
A plug-in like that alongside a script that allocates all the posts on the blog then manually writes into the plug-in's database table, that might work as a much uglier workaround.