Hi William,
You have two options here, once you have queried LDAP:
1) you can return the results as a String or a collection. In order to show them on a form you can simply add the results to a multiline of text.
2) However if you want to save them in a repeating field this gets a little more tricky. Best thing to do is create a repeating field on a form and map the field to a multiline of text, save an example and check the form data for the XML format that it saves. You would then need to recreate this XML in the workflow with a build string function and loop through the collection of groups, aadding relevant XML as you go matching the repeating field XML. This will add all groups to the form in the repeating field
Let me know if you need some kind of example.
Craig