Yep. There is a trick that currently makes the round.
Colonise the holy world, pause the game on the exact game the colony is completely set up (slow the game down to very slow to do this), offer the colony to the overlord as a gracious gift.
The Fallen Empire will be angry at whoever holds the colony on the end of that first day. The AI has no reason to refuse the planet (if it was holy, the FE would either have shrekt you and taken it back or it's already rekt and the world is free for all), so it will love you for gifting it a free planet (maybe you need to throw in some free minerals per month for 10 years or something

), after which Fallen Empire senpai will notice them.
Wait for them to get stomped, declare war immediately after they get out from under big daddy Holy Guardian and send fleets just big enough to stomp all their star ports to each planet - take the star ports out, reunite your fleet to take out whatever the Overlord might have managed to save from the Guardian/squeeze out in the meantime, then take your time slowly bombing and occupying the planets (which should all have a corvette in orbit "bombing" to keep them from building ports).