Undoing Compressor

[steve]

Could you counteract that by reversing the audio and then using SC4, and re-reversing

Yes, but that somewhat defeats the point. If you want a compressor with lookahead, use a compressor with lookahead. Compressors without lookahead (or with lookahead turned off) can be used creatively to great effect (but not as a peak limiter). For example, if you have a bass guitar and you want to keep the attack, but compress the sustain, then you could use a compressor with a fairly slow attack and no lookahead, thus keeping the transient peak of the initial attack.