I have Esge fenders on one road bike and Zefal fenders on a beater rigid MTB and both sets came with a thin stainless sheet metal clip for the rear fender mount. The clip has nearly no bulk and you "custom-bend" it to hold the fender when you install it.
You might see if your LBS has or can get one of these or if you can make a similar bracket as they are much less bulky than the PB version you show.