VRA 7 - Finding Directory User via "custom" synced user attributes in VRO

Has anybody found a mechanism to find/filter by criteria on custom synced properties for Cafe Users? (or anything other than account name and given name for that matter)

See specifically getPrincipalsByPrincipalSearchCriteria(...).  It does not appear that the string criteria allows for search strings that provide attribute based look-ups. 

We can get user objects based off of account name or givenName, but the criteria object doesn't appear to be able to hold something along the lines of...

MyDirectorySyncedCustomAttribute == "FINDME"

Example...

var principalSearch = new vCACCAFEPrincipalSearchCriteria(tenantName);
principalSearch.setDomain(domain);
principalSearch.setLocalUsersOnly(false);
principalSearch.setCriteria(searchTerm);

var client = cafeHost.createAuthenticationClient();
var service = client.getAuthenticationPrincipalService();
var users = service.getPrincipalsByPrincipalSearchCriteria(principalSearch);