Theres always the reprolabel faceplate filler...
Comes in two layers. One thick sticker that evens out the contours on the mouth and a cover sticker that goes over the whole face and emulates the full covered look. It works well. I havent used mine though because i like the mouth design. I think the sticker sheet on total comes to 19 cad. It also gives you the whole range of accent pieces and autobot logos to make the figure pop.