rotating ad groups that don’t allow certain sponsors to appear at same time?

On our site, sonicscoop.com, we have 2 ad areas – the leaderboard (1 large ad, using Ad-Minister plugin), and the sidebar (6 small ads, using Ad-Rotator plugin). Currently the ads are shown randomly, but I also want to add functionality that will disallow competitors from having their ads shown at the same time. For example, if a recording studio ad shows up in the leaderboard I do not want to have another recording studio showing up in the sidebar.

Does anyone know of any way to do this using Ad-minister/Ad-rotator, or any other plugin setup? I looked at a lot of other ad rotating solutions but none seem geared for this. I’m thinking it would be some sort of custom PHP script that attaches an ad-group variable to each ad in the leaderboard rotation, and then the sidebar plugin would add a function that says “if ad-group=x, don’t select an ad from ad-group x”.

I’m still fairly new to PHP so I don’t know exactly how to implement that. Also I’m not sure which types of ad rotating plugins would allow for variables like that?

Any help would be greatly appreciated!