If the INGROUP function only queries the groups the script initiator is a member of, then another method like querying AD for user membership, then using the results in an array may be a work around for your situation.
I'm not intimately familiar with the LDAP querying UDFs, so my recommendation was more of an impression of what may be a good direction for you to go, rather than an authoritative suggestion.
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let the wise listen and add to their learning,
and let the discerning get guidance- Proverbs 1:5
