I think you'll do better better gold/hour doing the Grizzly Hills dailies; although that's limited in how much you can make per day it sounds like you have another team you're working on at the same time.

The idea of grinding leather as a multiboxer makes my teeth hurt. Stacks of Borean leather go for under 8 g on my server. Farming it outside of instances is gonna be very inefficient since you'll only usually get 1 per mob and you are limited not by firepower but tethering in pulling multiples. You can probably make more money farming some rugged leather on your single pally in dire maul north than on your team farming borean.

I guess if I were going to grind mobs for money, I would do so in storm peaks; now that the relics of ulduar aren't soulbound,they sell for a pretty ridiculous price. You're still gonna be mob-starved as a multiboxer, though.

The Relics of Ulduar page on wowhead has a number of suggested farming locations:

http://www.wowhead.com/?item=42780#comments

Some of these may require a flying mount; not sure as I was flying by the time I got to storm peaks.