How to Route Electric Guitar to Speaker Out and Acoustic to Main?

Hope someone can help me configure a way to do the following with my Power Rack:

I use a Lehle 3at1 to switch between electric and acoustic guitars, to a common output connected to my KPA input. Either guitar goes to the Main Outs but I also want to monitor my electric guitar (not the acoustic) through my onstage cabinet linked to the Speaker Out. At present, both my guitars reach the speaker. The only way I have found to keep the acoustic signal out of the Speaker Out is to send the signal on my acoustic rigs to the FX loop Send and route that separately to the FOH mixer but then I lose the stereo imaging on my acoustic rigs.

Is there a solution to this?

Quote from Kemper Support #1

you can assign an expression pedal to control the level of the monitor/speaker output exclusively. The level that goes to the FOH will be unaltered.

Thanks but as I chop/change quickly between guitars during songs I don't have time to engage a pedal at the same time. I need a hard routing solution.