According to Bob:
The Levelizer compressor set at -inf ratio with 0 attack and a release about 150-250ms works very well as a clean brick wall limiter. Adjust the threshold down to the limit point and it should do a good job of keeping anything from getting past that level and still sound clean while smashing the signal if needed.
The Levelizer must be patched posr fader on the output chan as the last thing in the signal chain.
Note: The Peak Limit / Normalize functions cannot be used with SAC