I think I've found what may be the easiest way to solo on a druid. Note: not fastest, not most efficient (although it is pretty mana efficient) but it is VERY easy. Basically the premise is you become a psuedo-lock, and it only requires 11 points in balance.
The shot cycle is root - insect swarm - moonfire - rinse and repeat. If you have a lot of spirit (which I've got as I'm resto) you regen mana like crazy with this, and as 2 of my 3 abilities are instant (and 1 I can get immune to pushback) it's pretty easy.
I was soloing the darkened spirits in nagrand (spawned from the "what the soul sees" quest after one of the auchindoun quests), and would be at < 20% mana almost every fight, now I end fights with > 80%.