All you need is:
piece of PVC pipe (10-12cm is enough) diameter depends of tire size
piece of steel/alu strip (to make L shape pieces, alternatively you can buy them ready)
some screws and nuts, also plastic wall plugs
piece of steel rod (insulation tape heat shrink or plastic pipe) I've used shop basket handle as a source
drill and bits
At first of all cut the pipe to two half pipes.
Drill holes in the half pipes and attach angle bars by screw
Measure distance between bicycle hubs and drill holes in the wall so the distance center-to-center of the half pipes will be the same
Now you can put the bicycle on the rack and figure out the position of eyelet, and attach the eyelet by wall plug and screw.
put the bike on the rack again and measure rod length (add a bit of clearance 1-2 cm). Bend the rod to shape on the picture or just hook if you'll have enough clearance.
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