I just made some spacers and extra long tube nuts and mounted an extra 53t chainring between the regular big ring and the crankarm. It just fits. Clearances may vary between types/models of cranksets. Had to use a 53t as the crankarm tapers in so there would be insufficient clearance for a chainring much smaller than this.
Of coarse this is just a lowly C'dale but it is what it is.
BTW I would be surprised if any of the other bikes on this thread are any more rigid than this. They are of coarse lighter though.