Lock and Mage Leveling Duo Advice Requested

I am leveling with a friend who is a frost mage. We're both nearly 26.

I initially started going with the obvious recommended affliction build, but then realized that if I could get my Voidwalker to the point he could actually hold threat and stay alive a bit there would be some synergy.

My current build is 5 into demonic embrace and 3 into Improved Voidwalker in the Demo tree - 5 improved corruption, 2 life tap, 1 drain life.

But I find that the resource juggling stuff in the affliction tree is kind of pointless. Instant corruption is a must but otherwise I wonder if I maybe should actually go hard in the destruction tree to match the quick burn style of the mage? Is it worth doing a weird build like that, assuming I'll be duo leveling with the mage and then when we do dungeons my own DPS being slightly weak - but that not being a deal breaker? Should I maybe take some points in suppression before going into destro? (of course this idea requires me to respec since I've determined that the life tap and drain life points are a waste).

In any case, assuming destro is viable considering how I'm leveling, what build would you recommend, preserving the necessary points in demo to make VW a somewhat viable tank.