How would you recommend securing a pannier rack on a bike without braze-ons? My bike has lugs for mudguards/rack down by the rear drop-outs, but not in the usual places at the top of the seat-stays.

My two options seem to be:


use P-clips around the seat-stays
fashion a single bracket extending from the centre of the rack to the bolt-hole on the rear brake bridge


The first option seems easier and less fussy, but perhaps there's another way.
The two options you mention are widely used.

Another option is a seatpost clamp with rack mount points
There are a variety of makers and styles, here is one example.