How to flash a custom recovery with heimdall (without touching the main system)?

The first recommended step in [the installation of CyanogenMod on Samsung Galaxy S](http://wiki.cyanogenmod.org/w/Install_CM_for_galaxysmtd) is flashing a custom recovery like ClockworkMod or the one from Replicant with a command like: heimdall flash --kernel path/to/recovery.img Now I feel that the instructions might be misleading: I have done the first step wanting just to have a custom recovery mode, without proceeding to replacing the main OS on the device. It seems I have done that wrong, because the device now always boots into the recovery mode. What would be the correct heimdall command to just install a custom recovery system without touching the main system?