XF 2.2 How to (cleanly) inject a custom post into a thread view


I'm trying to create a "sponsored post" in a thread view that uses a "sponsored" account profile, and then shows up exactly like all the other posts in the thread except that the content of the message would be an ad. So custom HTML or JS. The sponsored account would be an actual account with its own signature explaining that the content is from a sponsor of the website.

I used to be able to do this in XF 1.5, but on 2.2 everything has changed. The code to make a simple post is quite complicated now, so I am looking for any advice. I could copy a bunch of compiled HTML around, but that wouldn't be very maintainable so I am looking for a clean way to do this. Any help is appreciated. Thanks.