Hello Mathias,
I'm not aware of any command line option to enable ECC.
The default CodeWarrior project start-up routine INIT_Derivative(void) only initializes the internal SRAM prior to ROM->RAM copy-down. This should set ECC to a defined correct value that matches with SRAM content to avoid ECC exceptions.
If the default SRAM access timing doesn't match your needs you should add your custom init. code e.g. (PLL init/Wait states) into INIT_Derivative().
regards,
Stan