If the column doesn't work until configured, why add it to the list of available columns at all (until it has been configured)? The column isn't really defined yet, so it shouldn't be listed.
Presumably you would also want to be able to have more than one column, if it's dealing in configurable regex? If so, you would want a UI for adding and defining what the columns are. (Similar to the one in WowBagger's script Column - Custom Text and Regexp ).