While working on the Kharn model I decided to put together a wet pallete to help with the NMM blending. I took an old blister pack, cut a sponge, and picked up some baking parchment at the grocery store.
Now I'm in love.
The paint not only stayed wet while I was working on the model for more than an hour -- but when I came back to the den after dinner and a movie... yup, most of the paint was still wet.
For any blended colours this technique is going to be invaluable.
Thank you, internet!