JSON Forms - Loading select box options with async queries

I am using JSON Forms and I need to load a list of  users full names dynamically into a select box,

I select the users with  RoleVault.getUsersToRoleAssignments(......)   and I get many DN of users,

for every DN, I need to select his full name and add it into an array,  so that finally I will set the select box values by the array.

My way to insert values into the select box is : 

instance.setFieldValue(activityUsersArray,"recipientDn","recipientFullName");
The problem is that the "RoleVault.getUsersToRoleAssignments" and the function that get the full Name by the Dn are async,
so I don't have a way to ensure the array will contain all the full names and no full names have been overridden during the process.
Is there a way to do that?