It was always my intention to have a fender stay that was as discreet as possible, with it preferably running under the fender once attached.
My solution was to grab one of the Triumph fender stays that Steadfast Cycles sell.
Unfortunately it was way too narrow to suit my application, however, with some careful re-bending it now clears my 4.5 x 18 Firestone tyre. It was also way too short to clear the wheel, so I decided to give myself a flexible fix. This called for some 10mm threaded rod and rod ends.
Now I have an adjustable fender stay!