Try it in a DAW first.. use two copies of the same audio track, one as a key and the other as the actual audio file. Nudge the key track slightly forward and observe how the compressions sounds ... a hardware comp will likely react slightly different than a plugin, but not -that- much different. (you can nudge "left" both audio and midi key tracks..)
Alternatively, if you want more control, use a -delay- plugin on the -audio- track. http://www.voxengo.com/product/sounddelay/ (This will f++k-up all your PDC schemes, the "nudge left" approach won't)
Now, this is getting more serious and modular-like...