doing it jury-rig is always possible .. a buckle and strap [perhaps with a side release] will be tidy and secure ..
do insure the loose ends wont get into the spokes ..

The mount of my Beckman bags [example of detail planning]
used a buckle with a finger loop to pull it tight and a velcro patch on the strap and back of the Bag to secure the loop end
the strap went down under* and back up so pulling strap tight pulled the hooks down

*racks in this case was Bruce Gordon's