I would suggest seperating the calliper from the piston, remove the 4 * bolts pictured below

You don't really want to be separating the caliper halves. Whilst not relevant on these particular calipers, on opposed piston calipers, they are assembled in a jig to ensure absolute alignment between halves, for the internal fluid passages.
Don't know why the entire caliper aint painted though. I'm sure that the S3 and R32 calipers are fully painted - though if I'm wrong, just a small slice of humble pie, as I have dodgy guts at the mo!
