Don’t do that. Create MIDI In Blocks that receive only from your keyboards. For example, here’a MIDI In block that only accepts messages arriving on MIDI channel 3 and it will CONVERT those messages so that they use MIDI channel 1. Your plugins just always be on MIDI channel 1.
Note that once you have configured such a MIDI In block you can save it as a preset to make it easier to create new ones as needed without having to configure everytime (see the documentation)
Don’t do that 
Use multiple MIDI In blocks and do your splitting inside Gig Performer. Leave your MIDI controller on the same channel ALWAYS.