| I'm not sure of the spec's but apparently you can use the 'prillia RSV rear caliper and master cylinder. Both use bigger piston sizes. I'd guess the rear caliper is a 34mm (ST?) rather than 32mm and the master up to 13mm from 11mm??
The discs and caliper on the RS monster are also bigger so maybe a parts bin raid could sort it? You'd need the RS carrier to though.
The pad option Ray mentioned maybe worth a look at to, along with maybe a wavey type disc? | 
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