Hey El, one thing about crazy ideas is they help your overall understanding of how things work. There are lots of ways you can rout signals with a mixer, the possibilities are limited by the mixer you have. More expensive desks generally have more options/features.
Your idea is easier with mono input channels. e.g. make ch 1 MP1 A, ch 2 MP1 B, pan ch1 L and ch2 R either use ch2 insert (if your desk has ch inserts) for send rtn of eg (or any mono effect), now desk main L is dry and R is eqed/wet, although eq isn't usually referred to as wet, wet generally refers to other FX (mostly time based FX (pitch/chorus/flange/phase, delay, reverb)). In this setup you could use ch2 FX send(s) to eq/FX etc, return them in mono into other channels (3,4,5 etc) and pan the returns R. Again you end up with L dry and R wet. Other ways to do it is by using sub groups (again if you have them), you can use the subgroup outs directly or assign them to L R main as required. Some desks have inserts on the sub groups (so eq or FX can be applied there), some desks have inserts on the main outs (this is the most common place to insert eq for live PA). Channel inserts are more commonly used for additional eq (snare/kick) or gates (for drums), compressor for vox or bass, or you can change the insert lead wiring slightly and use them for a direct out (as direct outs aren't as common on smaller desks).
In case your not familiar with inserts, channel insert points are a stereo jack just after the input gain. Insert leads are stereo jack (tip ring sleeve TRS) to 2 mono jacks (TS). the send is usually the tip and return the ring, earth (sleeve) is common to all. So the insert lead breaks the signal path, the jack connected to the tip goes to eq/FX etc input and jack connected to ring the output (so now the device is inserted in the channel signal path). If you wire the TRS jack so Tip and Ring are wired together and use 1 mono jack (so mono jack tip is connected to either tip or ring) you can use the insert point as a direct output (e.g. plug into recording input). Because tip and ring in TRS jack are wired together, it doesn't break the signal path.