Field Group with user object

Is it possible to have the field group take care of a user object?

I have a field group with many text fields, which when committed, updates the DB as expected.

private JPAContainer<com.vaadin.demo.dashboard.domain.Meetingstudy> studies;
...
studies = JPAContainerFactory.makeBatchable(com.vaadin.demo.dashboard.domain.Meetingstudy.class,"dashboard");
..

fieldGroup = new FieldGroup(studies.getItem(meetingStudyno)); 

Meeting studies has several properties, one of which is a User class.

If i do something like this:-

Field sPreparedByUser = (Field<?>) fieldGroup.buildAndBind("preparedByUser");
            
It complains that the presentation converter is not available, which is correct. I don't want to display it per se, but do want to be able to set this value using a button and only have it update the DB wheni commit the Field Group.

Ay suggestions?