Hadn't heard that, but this recent quote from Keith suggests he might be playing on more than just 2 songs:
It took us all, and himself, on another journey, but it was great to have him playing with us last year; I look forward to spreading that around a bit. Ronnie [Wood] and I, you know, we’re two guitars in the Stones, and on the records, there are at least four or five guitars, we overdub and overlay and overlay. And to have a third guitar in and add somebody else for flavor, to us, it’s a sheer luxury.
http://www.suntimes.com/entertainment/19301626-421/keith-richards-calls-chicago-a-musical-heaven-for-the-stones.html