As many people have said, multidot 4tw. If your lowbie group can AoE the packs down quick enough that your DoTs aren't getting the chance to do enough damage, then ask the tank to pull more since you're all geared to the heirlooms anyhow.
Pardon, what mana issues? I assume we're talking shadow here. Replenishment and Dispersion not enough for you?! Manafiend will come soon enough too, and if you're still having mana problems, I don't know what to say, go drink a mana pot?
OT, it might be annoying to not be able to AoE until 75 but you're hardly handicapped for it. Multidot.