Whoever this problematic DD is, if they don't have /nin or /sam, can they go /thf? TA is an adequate and useful means of helping keep hate on you, plus improves the damage you can do with Atonement earlier in the fight. Even if that particular DD can't, do you have another who can? A thf or sam/thf can hugely help the hate balance in that type of situation. For that matter, keep the thf main in the same party as the problem DD and have them constantly Collaborator them, along with TA'ing you, so that said DD doesn't take as much damage.
For other suggestions, what I do probably won't help you as much since you're elvaan. I'm taru, and have 672 MP in standard melee gear while /nin. I tend to spam Cure IV's as much as the mages, which is where a huge chunk of my hate comes from. The other pld in my group has about half that, and I suspect you have a similar amount, which makes cure spamming a bit more difficult. However for zones where you get regular Restoration chests you can do about as well; your MP is there to be spent, so be liberal in its use.
Another suggestion depends on what job the problem DD is, and how strong your other DDs are. My other main is mnk (which absolutely destroys most limbus mobs), and I -always- use /nin; I tend to end up tank with that for at least half of all fights regardless of the tank or other DDs (excepting when one of the other good mnks we have is also there on that job). If you have someone like that who can flat out tank through raw damage, and is good at tanking while doing so, you have a good option for splitting the parties based on who you want to have which buffs.
You mentioned cor, but not brd, so going with just that, set the base party as pld+whm+rdm+cor+DD+DD (the stronger DDs that can best help tank), while seconday party is thf+pDD+smn+other. Improving the buffs for yourself and the tankable DDs keeps hate on you more; thf can Collaborator the problem DD, and their lack of buffs means they both have lower hate levels overall anyway. Smn in the second party for light curing and buffs and such; they'll have to do without Refresh, but Sublimation from /sch, plus Elemental Siphon, should easily keep them going.
In general, in fact, you want whatever DD buffs you can get. We tend to have a brd more than cor in our group, and I'm pretty much on double March 100% of the time. That may actually be another issue for you as /nin; if you have no brd, and no Homam gear yet, you'll have a real hard time with recast timers. If you're spending too much time casting ichi, or not having any shadows at all, then you lose most of the benefit of doing /nin in the first place.
Edited, Mar 5th 2010 4:14am by Kinematics