meh, dual wield may not "smell right" on rdm thematically: but it's a thing that already exists, that would go a long way towards solving one of RDMs problems. and since DNC, THF, and BLU got it, precedent has been set. it's an easy answer with very little reason as to "why not?"
other, slightly more complicated ideas would be:
-a job ability like diffusion or accession with, about a 3 minute recast.
this would allow for one spell to be shared full-time in potency gear, but not 2 even in duration gear. (it would be close though...) the big candidate here is temper, but gain/enspell/phalanx could all be useful given the right circumstances.
and
-an enfeebling spell that DIRECTLY reduces the damage of mob special attacks.
something akin to scherzo/earthen armor. the duration/recast would need to be such that it is full-timable. this would probably work a little differently because it's on the mob and not the players, so how does it check for hp%?
i would say make it reduce ALL the monsters special attacks, but by some lower amount. 25-30% compared to scherzo/EE at 45-50%? i think this would actually be fairly well balanced since the reduced potency still means you'll want scherzo/EE sometimes, but the lack of an HP% check means it can protect you from things scherzo/EE don't.
it goes without saying that this would have to be a reliably LANDABLE spell. nobody resists scherzo.