Hi,
Been gone for a year!
Anyway - we ended up renting bikes in Stockholm. It was cheap and so fun!
They have a different way to lock their bikes - there is a sliding key-lock thing which immobilizes the rear wheel. No need to carry a lock since it's built in (though we always chained them up too, since we didn't want to pay for the bikes just in case).
If anyone wants more info, I can find it.
Brian