hmmm good question, photocopying the decal and using it as a template for a mask might be a good way to go.
you can make a two piece mask with it, lay the decal copy on some frisket film or wide painters tape, cut the curve you need, that is one side of your mask, you want to be sure it will be able to lap OVER the nose (i.e. you want to go over the 1/2 point a little so the mask will overlap) then do the opposite on the other side of the frisket or tape. (this is how the pre-cut masks for canopies do on canopies with rather sharp curves like that nose) THEN, take that decal template and get it exactly in position where you want it. lightly pencil the outline so you know where to lay the edges of the masks...
I know that might not make much sense, if you need me to I will draw it with my poor artistic skills. Better yet maybe someone has a pic that can take of a precut canopy mask which will give you the exact idea I am thinking of...