Applying decals/patters to rear wing supports on Toyota GT-One

Can someone please guide me to somewhere I can find out how to apply decals and art to the side support stays on the Toyota GT-One,

I can change the colour, that’s no problem, but can’t apply decals no matter what I do. I have “painted” the “wing” a tonal shade different to main body as well… This is required to go along with my overal theme.

I’ve checked other painters efforts and seen that it can be done, but for the life of me, I just can’t see how…

Any help would be most welcomed indeed… Cheers.