A few years ago I read a book on using real estate as your IRA. It's a complicated set up, including starting an LLC (IIRC), attorneys, etc, etc. I found the book in the library, just google variations on "REAL ESTATE AS AN IRA" and I'm sure you'll find the info.
I walked away with the idea if you have a ton of properties, it would be worth the headache. Hope this helps.