Developer Nathan_r32_69 released a tool yesterday to allow people on a CFW to sign in to the SEN (a.k.a. PSN) by spoofing the necessary information.
People running a CFW on their PS3 can usually not connect to the SEN since they do not have the latest firmware. In order to be able to log in to the Sony network from a CFW, some information needs to be spoofed on the device, and this is exactly what this tool does.
Please note that using a CFW is against SEN’s T&C, and if detected, this could get you banned. Yup, I know that some of us want to run a CFW and *still* be honest customers wanting to buy their games, but apparently Sony is against the idea… so just so you know, you access SEN on a CFW at your own risk
SEN Enabler-disabler is compatible with most PS3 Custom Firmwares, including the DRM-dongle ones.
Download and instructions here.