You need to compress program or change bigger CPU.
Since FB's are multiused, I would think that it would be easier to check FC side if there is same FC -blocks which could be changed to FB/DB and save little bit memory.
Also Karnaught mappping and ST-coding helps save memory.
And if there is calculations, maybe you can change them so that not all is calculated on same program scan.
Would it use then less work memory, since not all code is executed at one scan cycle
Easiest would be change to bigger 1200 or 1512 CPU series