A custom field type multiselect containing a selectable pre-defined set of users

I would like a field type added to the Custom Fields that allows me to create a multiple select field that is populated with a list of users from a specified Group of users. Currently, the workaround is to have a Multiple Select field where we have to manually add/remove each user to the list. This in turn requires JIRA to be reindexed. It would make more sense to have the a new field type that allows us to configure a Group of users without having to reindex the application.