In an announcement made on the official City of Heroes forums it has been revealed that attendees of HeroCon later this month will qualify for guaranteed access to the Going Rogue Closed Beta.
Of course, there are some basic stipulations, such as the fact you must be over 18, a US resident, and not work for any competitors or their affiliates. You'll also be required to maintain an active City of Heroes account throughout the entire Closed Beta in order to access it.
If you meet all the above requirements all you need to do is sign the NDA agreement at HeroCon, and you're good to go!
Tickets to HeroCon can be purchased here.