Check here: http://www.ami-forum.de/forum/
(More experience there with those Euro conversions)

You should be able to get a Aftermarket Cat Installed.   Usually it's quite
a bit less then getting a OE cat to put on.   On my 1977 Chevy C10 I used to
have.  It had one of them pellet Cats on it.   It also had a screw on the
bottom of it which I removed and Started the truck up and blew all the
pellets out.  So basically a Empty converter.   It always passed the smog
test no problem.   If you can cut it out, knock the crap out from Inside and
weld it back up.  You should be fine.   People do it all the time.   Getting
a Muffler Shop to do for you may be a problem.   I hear in California it's
now a 10,000 fine.  Last I had heard is was a 2,500 fine.   If you do happen
to fail the smog test, it's not a HUGE deal you'll just have to get a new
converter installed and retest.   They do happen to brake up and blow out on
there own into the muffler if they get bad enough.