Sync LDAP Groups through several LDAP Providers

I try to solve an issue with LDAP group synchronisation.
The LDAP is an AD.
I have the Situation:
There are 3 diffenerent LDAP providers configured.
The users are synced from these three LDAPs with different priorities. This step works.
The LDAPs are federated and trust each other.

Now we have the groups:
There are only set in the main LDAP we call him MASTERLDAP.
The groupmapper is now set in the MASTERLDAP settings to connect the users which are imported from all three LDAPs to the group which is delivered only from the MASTERLDAP server.

Is there a way to add the users, which are deliverd in the group from the MASTERLDAP, identitfied by their sAMAccountName, to the group even if they are from an other LDAP provider.

Little Push. Does anybody had the the same problem?