Could coating silver inside of a cuvette be used for SERS?
from theory this should work what you have scatched here. When it comes to SERS a main point is, that you got a surface which is rough enough that you can create mini hot-spots for the electric field. This will give you the enhancement.
Maybe you must put a little bit of work in you set up. The scattering is needed to arrive at the detector. maybe you try a Raman probe or do a other angle for the wall with silver on it.
Best regards!