ericd in the case of damiana it is water soluble. One of the most common methods people consume it is in tea. Although if he wants to make it strong enough to get it's euphoric abilities he will have to make it taste very strong. Since at the strength most people drink it. It's fairly strong...
I personally would go with beets. They are very bright red ,add sugar & nutrients for the yeast. Plus as long as you don't add to much they add a nice flavor.