This would be an additional speakers correction module.
Something like the "Speaker Mode" in Breakaway Live.
But it would not make sense for the existing EQ (post or
pre Multiband !) to have separate left/right channels IMO.
This EQ is not meant for speakers correction.
It is there (using before/pre option) to dynamically equalize spectral differences between different sources (especially old music vs. new productions, etc.).
So, really what you want would need an additional module.
I don't know what version of Stereo Tool you use ?
If you use the DSP or the VST version you can alternatively use the free easyQ VST plugin post Stereo Tool:
http://www.rs-met.com/freebies.html