I just got these awesome Wald rear folding baskets as an early christmas present from my Girlfriend. The hardware they came with will not fit on my Batavus Fryslan Rack. What would be the best way to mount them?
After posting this question, I got a twitter response from my local bike shop where I got my Batavus. They suggested screw clamps, and I agreed it was the best choice and mounted my rack with them. Urbanistic tea and bike is awesome!
This video really helped me with a milk crate mounting. Using the same concept with nylon string, I would expect you could attach your folding basket, only attaching to the non-moving portion.
I would use a combination of baling wire and zip ties. I never rely on zip ties alone in a load bearing application. Zip ties will hold the basket tight and the baling wire will act as a failsafe. Use a load rated zip tie and inspect attachment points regularly. Replace zip ties as they break.
Alternatively you can probably find larger p clamps at your local hardware store that will fit your rack.