A supersusan, as I use the term, is a large circular spinning tray that rests on a shelf. Most people call a supersusan SET by just the name supersusan. It is two supersusans in the same cabinet.

Supersuzans, in this meaning of the word, have to be built into the cabinets when the cabinet is manufactured. The cabinet box must be built, then a single susan dropped in, then the shelf placed in, then the second susan. The susans are too large to fit through the door opening into the cabinet.

If you buy a single susan you can drop it in from the top before put on the counters. That would leave you with a susan on the shelf above and a normal shelf below.

Supersusans cant be retrofitted after the counters are in place.

However, there are a variety of regular lazy susans that CAN be retrofitted into the space they are just smaller than the supers becasue they need to fit through the opening for install.

Do you know what kind of susan you are looking for? The kind with a pole or a kind to be placed on a shelf?

I did this project once; it was a super pain, but they were just regular lazy susans. You might have an easier time, since it's yours and not a customer's... That aspect added a bit of drama...
This article was one I wrote after talking to a Bertch R&D guy. I talked to him a couple weeks ago. It's been over a year since I wrote the article, and he was still laughing at me.
The only thing I'd recommend that didn't in the blog post is that you might want to remove the hardwood pieces. One of them I was screwing with got a bunch of little dents in it.

Here is a link that might be useful: How to install a lazy susan after the fact