Have soloed and killed everything up to and including past Fineus Darkvire a while back, but time constraints stopped me moving further and haven't been back in.
Must try again some time :-)
BTW - no spec change - this is as a 0/21/40 Lock.
But basically, there are two things that are your best friends here:
1. The big blue guy used carefully will give you what you need with careful pulling, even with larger packs.
2. You can sneak past a few more problems than you might anticipate, although I must admit half the fun for me is killing everythig.
Take enough shards just in case :-)
Next biggest problem is bag space for the loot - may not be highest value stuff - but I hate throwing it away :-(
LBRS is also quite easy.
I am sure that with a demonology spec and the availability of the felguard as well as the better VW these would be more fun :-) (I should try a respec during a raiding quiet period)