It has been found that GCCE build have generated huge binaries.So to trim them a bit just include the following lines in your .mmp file.
OPTION GCCE -O2 -fno-unit-at-a-time
And viola you would get a considerably smaller size binary. Just to tell you how much this helps,I had 47 source file project,which linked with around 30 libs.This binary size with optimization OFF was a whopping 101Kb and with optimization ON it was just 51 Kb. Also remember if after putting this option you do not see any difference in size,just remove the .o files from the [epocroot]\epoc32\build\[prj_path]\group folder and run the command again.