I think that the problem you are having is because of how the radio option is set up. Currently you have the radio option inside of a repeat region. This is probably the reason that you can't see it when you select the lightning bolt icon.
One way that you can try to work around this is to remove the repeat region from around the radio element. When it is by itself you should be able to make the association with the proper cart column. Once you have set the binding for the column you should then add in the repeat region to make it have multiple options available.