You could do some light conversion - remove the plume & cover the helmet with a skim of green stuff or similar sculpting putty to obscure the details of the helmet a bit. Paint this the same sort of dark greyish brown you would a British Shako in a cover & you are done.
The Liquid green stuff Games Workshop sells to fix its
finecast ranges would be easier if you can stand the price as you could just paint it on with a nylon brush.
Ginger