Take a look at eval script #3 on that feat - you'll want to add some extra lines to that script - start with what's there, and then add more to the candidate expression - put what's already there inside (), and then add on " | IsWeapon.wGlaive", so that you can have a weapon that fulfills the normal expression, or it can be a glaive. (and double-check that wGlaive is the right Id for Glaive - I didn't test that).
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