RDM will give you Fast Cast and the same Magic Attack Bonus as BLM.
BLM gets it at 10. RDM at 20. It's just nice because you get the damage on your Ni spells as you would with BLM and you're able to throw Cure II's.
There isn't really any kind of Cure Spell that you'll have as a WHM that you wouldn't have as a RDM. Both get Cure II under 20. Both have Barfire/a.
I do the BCNM like I play NIN/RDM ballista. Melon Pie +1, Int +3 rings, RSE H boots (int +3 agi +3), cunning earrings. And basically any 40 cap gear you want. Forget the weapons. They aren't worth it.
Each nuke of mine does about 95-103 damage. (Suiton pulling down the only 103 I believe).
You are right in that /WAR has nothing. But oddly enough. Even NIN/WAR can do this BCNM fine. It's such a joke in terms of difficulty that even /WAR performs perfectly okay.