Have you tried launching the launcher via steam? Add non steam app, add launcher.
Also i remember some time ago when i was making a research for my friend, there are two types of CD keys. There are 5x5 and 4x4 keys running around, you can convert the 5x5 from steam to 4x4 from talewords forums. But i am not sure if this cannot somehow break your game in other way, so better to wait and check if someone has some experience.
Anyways, try to google the CD key conversion, maybe you will find some info that helps.
You can also try to hit the devs on IRC channel, cannot find the link as wiki seems to be under construction :S