After considering the option of using sports tape on my 18" WWII, I decided that it wasn't entirely appropriate. So I took some 1000 grit automotive sandpaper and sandpapered the handle, removing that varnish which makes the handle look so shiny.
This is the same handle after a bit of clean up with a wet paper towel.
The whole knife, with its new satin-finished handle. I actually prefer this finish over the previous one, which you can see below.
I will be looking for some lanolin in the morning, so I can treat the handle and keep it in perfect condition.