Custom Fields - How to hide an entry from the selectable list?

[brooklynbase]

Hello all,

Please see this screenshot:



I have created some custom field strings, together with some custom field plugins (the plugins are those that begin with "+++" in the screenshot). Is there a way I can hide the string custom fields from this drop down list without deleting them, so it only displays the +++ plugin entries? I tried ticking Hidden and tried unpublishing them, but they still show in this list.

Using Joomla 3.4.8 and Virtuemart 3.0.12.