How to insert ads at top / bottom of post (on a per-site basis in blog network)

Hey guys!

How can we display ads at the top and bottom of the post, individually on blogs in our multisite blog network?

Specifically, between the article headline and the beginning of the actual text content. And at the end of the actual text content.

Simple Ads seems to allow this - but that is made to run site-wide. We would need this to be possible on individual sites within our blog network.

Thanks!