Not that I can think of unfortunately. We go across several times a year as I have rellies on the island but the best we do is buy a "book" of six tickets which works out around 30% less. Not any good in your circumstance though.
Its one of the beauties of island life - getting stitched up by Calmac everytime you wanna go somewhere (with a car that is - pedestrian fares aren't too bad)
You're probably going from Ardrossan - Brodick. There is a slightly cheaper fare from Claonaig - Lochranza, but that's way off your route I guess unless you specifically want to visit Kintyre. Unlikely
WANTED: Kona Sex One rear brake canti hanger pivot thingy - GOT ONE!
I could be tempted by a 19" - 21" Dave Yates (mountain) frame.................and no I still don't do trail centreshttp://www.corrieyairack.org/index2.html