Don't the Rune items drain mp to the sound of 3mp/tic? If so, I guess you'd macro it in before a spell goes off, and just not idle in it.
RNG:75 MNK:75 WHM:75 BRD:75 BST:75 SAM:75 WAR:75 THF:75 BLM:75
DRG:72 SMN:63 DRK:55 NIN:49 PLD:42 RDM:41 DNC:37 SCH:37 BLU:37 COR:20 PUP:22
Woodworking:88 Cooking:60 Alchemy:60 Bone:60 Leather:60 Cloth:60 Smithing:60 Gold:54 Fishing:33