Count of Tuscany, yes, but I don't know that they've ever done it anywhere else. Not in the middle of a song. They usually get Jordan Rudess to do rhythmy guitar stuff, if it's really essential, don't they? They even had James LaBrie play the second keyboard in Octavarium, they're generally pretty hot on ensuring they make all the noises themselves where possible. I'm watching The Root of All Evil from the Dramatic Turn tour, under the solo - if there's any song they'd pump the riffs in, I'd think that'd be right up there, and they're not, it's just bass and keys.