Is there an easily-copied bodge that puts the rear light underneath the rear rack?...
I have a bodge for racks with a solid top plate. It creates a short post underneath the rack to which you can attach any rear light using the seatpost bracket.
Ingredients:
a plastic spool of sewing thread. Black, ideally.
a bolt, 15mm longer than the spool and narrow enough to go through its centre
a nylock nut to fit the bolt
a washer
Equipment:
a drill
a drill bit slightly wider than the bolt
spanner to fit nylock nut
marker pen
Method:
1. Unwind the thread from the spool and discard it. You just need the plastic spool.
2. Mark a point on the centre of your rack top, about 4cm from the rear edge. Drill a hole at this point.
3. Slot the bolt through this hole and fasten the empty spool to the underside of the rack using the nylock nut and washer.
4. Attach your rear light to the spool using the seatpost bracket.
With this bodge, the rack acts as a cage for the light and protects it from being knocked by luggage.
I used a roofing bolt which is good because it has a domed head. If you're beady eyed, you'll have noticed it's a square nut in the photos, not a nylock one. That's all I had when I put this together. To be replaced.