I have an iMac 11,2 and successfully installed the Mojave Patch
Boot the system in internet recovery mode to enable SIP. You can do that by holding down Option-Command-R while powering on the iMac. After booting, follow instructions similar to ordinary recovery mode to enable SIP. I.e. open a Terminal and execute:

csrutil enable


If you haven't got internet recovery on the iMac, you will need to install the updated firmware software that is available for your model first.