Is there an easy way to append a new contact to an existing group contact, without overwriting the existing dlist members?

Code:  zmmailbox -z -m gact -v
     "attrs": {
          "dlist": "\"Test1 User\" <>, \"Test2 User\" <>",
          "fileAs": "8:Zimbra Testers",
          "nickname": "Zimbra Testers",
          "type": "group" 
     "id": "1164667",

I can do the following, but it overwrites the current dlist members.

zmmailbox -z -m mcta 1164667 dlist "\"Test3 User\" <>"
I understand I can fetch and modify the 'dlist', but is there another method to just "append" to it?