I'm a bit late to the thread, but if the difference is "the same person is reading the ad" some of what i think are dynamic ads are being done in a similar way. most of the ads within podcasts i listen to are read by the hosts anyway.

When there are ad spots in the middle where i imagine it could be pretty easy to cut in an ad dynamically. Some podcasts do a little music fade in/fade out before and after an ad, which is usually a script or something from the advertiser read by the podcast host. I assume the the transition and ad are mostly done dynamically? although i have no way of knowing for sure.