A great addition would be the first three Genesis live albums. "The Knife" off Genesis Live, "The Cinema Show" off Seconds Out, and "Fountains of the Salmacis" off 3 Sides Live are excellent, especially with the added percussion in the last two with Chester Thompson, definatly a different twist on the original tunes.
I think the live version of "Lamb Stew" would also be great, I beleive a good version of that is on the 1976 Burbank boot, it will give AM listeners a good idea of the "Collins" rendition of "The Lamb Lies Down on Broadway".
"Ladytron" from Roxy Music's first album would be nice, and the cover of "Watcher of the Sky's/Firth of Fifth" by Transatlantic would also be great, I beleive that is on the Transatlantic Live in America CD or a boot.
AM is without a doubt one of the best radio stations out there. Keep it up!