Here's what I have done for similar situations:
Cut out the decal with the backing on to separate it from the rest of the sheet. Disassemble the gauge, and paint the raised areas with some sort of marking that will transfer. Press the decal gently over the needle post until it marks the outline of the raised part on the backing sheet. Cut the decal along that outline with a hobby knife, then peel off the backing and apply the decal to the gauge face.
