Drifblim @ Leftovers [pinch berry could also work, but is a bit risky]
-Baton Pass
-Stockpile
-Charge Beam / Protect [if leftovers]
-Ominous Wind
EVs:
12 HP
252 DEF
244 Sp. DEF
Safer and more balanced than my second suggestion. I'd suggest Ominous Wind over Shadow Ball because you're not training the Baton Passer to do damage anyway, and the 10% chance at boosting all stats could really help whatever you baton pass to. Protect in place of Charge Beam will allow for some extra leftovers support, and increases your chances of getting to baton pass more than once. Charge beam does supply a way to dent the ever popular PHazer, Skarmory, and dropping it means losing your offensive boost for passing.
My EVs, like Jet's, are balanced for optimal support from leftovers, but Stealth Rock will do slightly less.
Drifblim @ Salac Berry or Leftovers
-Baton Pass
-Calm Mind
-Substitute
-Ominous Wind
EVs:
252 HP,
252 Sp. DEF
4 SPD
Essentially one of Jet's suggestions minus Shadow Ball, but with different EVs. Since it's focused only on special defense, it'll take hits a lot better in that area, and I'd lean towards the Salac Berry to boost with substitute.
If you do decide you'd like more balanced EVs though, take a look at drifblim's stats. It already has plenty of HP, so I wouldn't recommend more than what you need for optimal leftovers and substitute [12]. Drifblim is really lacking in defenses, so training those will allow it to take hits better than training it in HP.
[EDIT]
Drifblim @ Leftovers
-Stockpile
-Ominous Wind / Shadow Ball
-Thunderbolt / Charge Beam
-Explosion
EVs:
100 ATK
122 DEF
200 Sp. ATK
88 Sp. DEF
Ominous wind can boost everything including your ending explosion, but Shadow Ball can give a bit more initial power and PP to work with. T-bolt gives a reliable attack, while Charge Beam will give you a good chance at raising special attack.
I'd suggest against using both Charge Beam and Ominous wind, but one or the other would be great for the set