One interesting way to approach this would be with the Gestoso MidSideEncoderDecoder prototype. We want to trick it into thinking that we are feeding it an encoded signal (as if it came from a mid-side microphone). To trick it into thinking that our mono input is an encoded mid-side, 2-channel signal, check the SkipEncoding check box.
In this example, I used a GraphicEQ where channel 1 is controlled by seven faders and channel 2 is controlled by (1 - <eachFader>) so you end up with the signal filtered one way for the middle and the complementary way on the sides.
If you open the Oscilloscope (from the File menu), select Outputs 1 & 2 and Left vs Right, you can see that the Mid is in phase and Side is in antiphase. You can use the !Mid and !Side faders to compare the two and to give them different levels in the mix.
This configuration gives an interesting way to turn a mono signal into a pseudo-stereo signal where the stereo separation is linked with the EQ. You can set it to put the low frequencies in the center and highs spread out to the left and right. Or the opposite. Or any arbitrary EQ on the mid vs the side. Cool idea!