Any COR's that want this and have MP merits, a simple (yet expensive) solution is a Cassie earring. You only need to swap it in for a fraction of a second and it will push your mp down by 50, so even if you have max MP merits, it'll put you at 30/100 with pendant on (take off MP+ gear when swapping Cassie in to push your MP down further)
@Prinnysmash - I haven't tested it, but are you sure that it would activate with just this item giving mp? Everyone says it has a to be a visible piece of gear giving you MP. Neck piece is not a visible piece of gear unless this item also counts itself as MP gear.
I would hope most COR's would be using Crimson/Blood Finger Gauntlets which is a visible piece of gear with MP+ on it. If you don't have mp merits and are coming from your MH just unequip them and equip them back. Problem solved. Hello +8 MAB on quick draw.