I really don't think an SR will pass CA emissions, cat or not. I don't think sr's have an egr, which is one reason the visual component is required on a test. I don't think any jdm cars have an egr for that matter. The egr lowers CO2 levels, so when my car was on the sniffer (with a cat), the CO2 was off the scale. Plus, every 240 I know of is getting those damned Test Only notices. Maybe you can weld two cats together (some cars come with two).
On a side note - I was reading the uk sr20 fsm and I think the UK sr's have an egr, which might make passing easier. It might be easier starting from there.
Just register the car in an area where smog is not required (except when selling the car). That would be in a gray area on this map:
http://www.smogcheck.ca.gov/ftp/pdfdocs/program_map.pdf
I thought about doing that, but it still won't stop some overzealous law enforcement officer from ruining my day with a ref ticket. I keep hearing that they're going to change this law, but it hasn't happened yet.
As far as legalizing the sr20 - I don't think it's gonna happen any time soon. We're all too poor to shell out the cash for that. And if I had that kind of cash, I'd have a BMW.