You can also go with one of these instead of a bullet button, the funky paddle that attaches to your grip to keep you from obtaining a "wrap around grip"
http://solartactical.com/AK-SAIGA-SERIES_c34.htm
also allows you to use pre-ban normal capacity mags, but that doesn't really help you out as far as them shipping without the magazine.
maybe you could have one of those shipped to them and ask them to ship you the magazine separately, in pieces, or just keep it? don't know why they're refusing to remove the mag.
solar tactical also sells a magazine block that restricts a 30rd mag to 10rd. if you could get them to install that, it'd be good to go.
or just buy it from someone like atlantic that has ready to go ca legal guns.