A person on the facebook group posted a link to
this youtube video a while ago which I followed and got some nice results.
Some things to note (mentioed in the comments on the video, the method doesn't work on animated objects (doors, bogies, running gear etc). You need to use m.reflect or similar for those.
I don't know how you could do it if the model already uses a bump-map
It can be very time consuming on complex models (like K&L, for example) and takes a lot of trial-and-error.
I'm sure they may be other, better methods from people who actually know what they're doing (not me) but it did allow me to get one thing which I have longed for, for ages, which is a K&L model with a rich, reflective finish. I may eventually do some more.
Hope it helps.
Cheers,
Piere.