I used dishwasher method many many times on all kinds of keyboards. I don' know how Das Keyboard works inside, but I'll provide some information on the dishwasher method, so you can determine if it's applicable.
Basically, inside simple cheap keyboards, you have plastic case which, a simple printed circuit board, several sandwiched plastic sheets with conductors which connect to the PCB and a piece of rubber which goes between keys and plastic sheets. Plastic sheets are often wended together.
The idea is to put the plastic case inside the dishwasher and wash it. I often clean the PCB itself with alcohol. Plastic sheets may be washed in dishwasher, but they should be left todry or they can work incorrectly. Since only the top sheet is exposed to elements, I usually clean only the top sheet with alcohol, since it evaporates quickly.
The "rubber" part often looks to weak to me for dishwasher, so I clean it with warm water and then leave it to dry.
The whole point of my exposition here is that the main damage which can be caused by dishwasher isn't to electrical components but is simply mechanical damage.
I've read this post and it seems that Das Keyboard is internally very different from classical keyboards. There is a picture of keyboard without key caps. To me it seems that the best way to clean the soda would be to detach the top part of the keyboard from the rest of the keyboard and only wash the top part in warm water or something similar. The downside is that you can easily wash away any lubricants that may have been used in the key assembly. Still, I believe that it is preferable to soda residue inside key mechanism. It is also possible that PCB will get wet, so you should let the keyboard dry in such position that air can circulate through the gap between keyboard and top part. Also, it would be smart to turn the keyboard few times while drying and to shake it few times because water can get into the small gaps between mechanical elements and stay there for some time.