I work for a company in the podcast hosting space and dynamic insertion in real time during downloads is something a few companies provide, including us. Actually one of our products[1] is just a "plug in your RSS feed and we'll give you another one with updated URLs which dynamically inserts ads during a download", so you can use a different hosting provider than ours if you want and still get dynamic ad insertion powered by us, since a lot of hosting providers don't have that feature.

[1] https://www.voxnest.com/dynamo/