The odds are stacked against you as a paladin OT. Without taking damage, we have to live on a very paltry mana income. That said, there are a few things you can do to boost your threat in such a situation.
Get BoW if you don't normally use it. If you're the only Paladin, use BoW. Keeping ahead of the dps will be harder than staying alive for most fights.
I support JoW, SoV, JoV (repeated). An additional JoCrusader is good if there's another Paladin available. Depending on positioning for OTing, you may be able to get a flank or the back to avoid parries altogether. More hits, and less interrupts like knockdown or stuns mean it is easier to keep a stack of SoV running. Consider building your stack while trinketed, as long as the stack stays up, you'll get the benefit of that initial spell damage figure.
Try to get thrown in with a Shadowpriest. A Shaman helps a lot too, for their spell damage, mana tide or windfury totems. Take a look at mp5 consumables like Flask of Mighty Restoration and Blackened Sporefish. You'll end up lower on tanking stats, but your sustained threat generation will be higher. Use a potion every time the cooldown is up, and use max rank consecrate whenever you use AW.
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http://armory.worldofwarcraft.com/character-sheet.xml?r=Medivh&n=Minn