Yes, this feature is missing in the FieldPlugin. Please add a new request on JIRA and provide us with a pull request if you wish so.
Here are some tips if you want to get involved: http://forge.jboss.org/docs/get_involved/contribute.html
Ok, thanks. I'll create a JIRA ticket and take a look at FieldPlugin and see if I can add the feature myself. If I can get it working I'll give you a pull request for my changes.