Give BLM Channeling abilities similar to how VIVI was able to use EN Spells on other players. Use this in conjunction with burst magic this ability can be set only to activate for characters involved in the initial Skill chain from which the burst was Created. Depending on the level and strength of the BLM this could Reach EN-3 type of levels giving it a bit more edge over RDM and Giving it a place in modern parties. Linking it to Burst means BLM wont become another buff whore, and limiting the time the resulting EN effect is active accordingly to help with balance. If you wanted the effect to be completely similar to VIVI in FF9 Then Give the Affect an Enmity bonus so blm's could select the tank as the ONLY effect recipient, and giving the BLM some extra room for a time limited onslaught until the Tanks enmity is returned to normal.