The THAT1200 line receiver opamps make it pretty easy. Designed by Bill Whitlock of Jensen Transformers. I doubt they are used in any domestic audio products though. Just an FYI if you haven't seen them.
Good point. The device you mention has 70 dB CMRR @20 Hz and 65 dB CMRR @ 20 KHz. Furthermore, putting the balancing resistors on the same chip means that they stay matched as the temperature changes, which is iffy with discrete parts.