Put it in mono, find the frequency where you filtered the bass before, make a note, use Waves Q10 to do a really really really sharp filter at this freqency, make two new files from the original stereo, one with the bass, one with the tops. Invert the phase on one of the channels of the top, mix the bass back in.

Use the cross-over presets on Q10 to start you off on the filter, select all the frequency ranges with the mouse (drag a box over them) to adjust the cut freqency.

Might reverse most of the damage, hopefully without adding too many artifacts.

Now to get a bit of width back you could use a touch (only 1.1/1.2) of Waves S1 imager before you merge the bass back in.