Hi Chris,
I have an Astronomik CLS filter I rarely use anymore as I haven't got the skill to restore the color balance in stars. I think with appropriate sub length it could be made to work. It definitely helps with the LP. It's a 2" screw-in type so if you want to borrow it for a while to see if it works for you send me a PM.
cheers,
Andrew.
PS - my astrobin site has a few images taken with it in place, notably the horsehead, M42 and M31 images.
http://www.astrobin.com/users/alocky/