If I'm right you have to retard your ignition by 2 degree for every 50shot of nitrous.
What's a good way to retard you ignition:
1. buy a piggyback (turboxs utec ($800), Greddy E-manage Ultimate ($550) )
2. or ECU reflash like Cobb AccessPORT ($500)

How have you people retard your ignition? Are there other ways?

 

meth/water injection

 

If all you're want to do is retard the timing by 2 degrees then ask your dealership if they're willing to do it. Some may charge, some may not. Alternatively, you could find somebody who has a Cipher or an AccessPort and use that to retard by 2 degrees. +/- 2 will be the limit with these methods.

That's how I did my set up and I throw in some race gas at the track.