What you need:
1.A length of chain, each link is 2cm wide by 3cm long (size for 700c tube)
2. Old 700c tube
3. Shoe lace or any strong thin string/rope
5. old button up shirt that you don't mind getting dirty
This is were the button up shirt comes in. button it up and put the chain through the shirt at around about stomach level so the chain is level.
Now you can pull the tube up over the chain.
Once you have pulled the tube right up to the top your done, YAY,
If you have some excess tube left over you can even stretch it over your padlock.