So the basic plan was: Let he who casts the spell, choose the targets.
There have been three addendums to this rule:
1 - If the spell screws me over - by killing kaervek, destroying my mana, discarding my hand, dealing me damage, etc - then I will choose the targets as I see fit, usually with intent to screw the caster over as much as possible. This is open to some interpretation when it comes to global effects like board wipes, which might be positive or negative depending on what my opponents are doing, but generally you know when you're doing something that's going to piss me off. Almost anything you're doing that's improving your own board position will not fall afoul of this rule - draw, ramp, tutor, whatever, it's all good. Just don't mess with me.
2 - I will not target anything that would be a very bad choice. Kaervek won't kill himself, unless there's some reason why that might be necessary (such as a control magic being played on him). He won't target me. He won't target a player with No Mercy unless it's for lethal, he won't target a phyrexian obliterator, etc. If you absolutely refuse to choose a target - which I can't legally make you do, since you don't actually control the ability and it's technically my choice...screw you for not playing along with Kaervek's "fun". You can eat all that damage all day long, you boring sod, until you either start playing the game or die abstaining.
3 - If the game is ending, or about to end, I will take the reins. When it's 1v1, I choose all targets, naturally. If I see a window to win the game, I'm going to take it. If you cast zealous conscripts with a kiki-jiki on-board, I will use Kaervek to prevent the game from ending by killing kiki. If you're killing the last other player bringing it to a 1v1 game I can't possible hope to win, I'll also prevent that from happening - though this is a somewhat grey area.
I've found this deck is actually quite a bit of very rakdos-y fun, and possibly the most fun deck I've ever constructed (I still hold up Phelddagrif as the best deck I've ever constructed, though). It speeds game up immensely, and it wins a pretty frequent number of games. It's certainly not without its weaknesses - it's very reliant on the commander - but when it does its thing, it can be very amusing watching my opponents pulverize each other only to realize that they're too low on life to fight off kaervek before he murders them.
This is not the optimized version of the build - that one is back on mtgsalvation - but this is what I'm playing right now, with some budget considerations in mind as this is my newest standalone deck, and isn't borrowing cards from my collection anymore. That said, it's still a blast to play even if there are some tweaks I'd like to make.
The essential composition is the same as ever, though - get Kaervek out ASAP with loads of mana rocks, protect him and make him as deadly as possible with enchantments and equipment, then watch the fun unfold. It also has some removal to keep up some interactivity even if Kaervek is offline and keep my opponents on their toes, and a handful of "standalone" cards that essentially are just great goodstuff cards that can do lots of work regardless of whether Kaervek is or isn't on the board, up to being win conditions in themselves, or just great value generation.