Sixty Fiver,
With my non folding R20 I've inserted a length of tubing up into the bottom of the steerer, drilled and bolted it where the original brake bolt goes then drilled the tubing at the appropriate position to use a Shimano short reach road caliper with MTB pads, it works very well. The Aussie R20 mudguards are narrower than others so with a bit of fiddling I can use them with these brakes.
BTW, over at the singlespeed/fixed subforum I posted my 100 mile ride of my SS R20 and you mentioned you were thinking of doing a long ride on your fixed R20 or P20...how did it go?