I found a cool trick that lets me jump between three gain stages in the same Rig with less tap dancing. It works in a few scenarios that you may use to get three gain stages.
Assign two drives to two slots, say the Kemper drive to slot B and the Full OC to slot C. Lower their mix to zero in base state, (which will sound the same as if they were both inactive.) Then hit the morph button and set their mixes to 100%. Then assign slot B and C to the same foot switch and turn off one while the other is on, so that only one can be active at a time
Now when you are in base state, it won't matter which drive is currently active, because the mix of both is set to zero anyway and the sound will be as clean as your amp is. When you hit morph, it won't matter that both of your drive's mixes jump to 100% because only one is active at a time. So if your lead sound is the one you use the least, save the Rig so that the B drive is active. Now you have all the advantages of assigning two drives to one footswitch, but still being able to hear neither. Keep in mind to that if you actually like using your drives with less than 100% mix, say 90% to let a little clean through, this still works. Just morph either pedal you want less than 100 from 0 to 90.
You could also do this in reverse. set their mixes to 100% in base state and 0% in morph. Then you can toggle between rhythm and lead in base state and hit the morph button to jump to clean.
A similar setup also works if you want to stack these two drives for lead, rather than turn B off when C is on. In this case, you still morph both drive's mixes from 0% to 100% but you only assign slot C to the footswitch, while leaving slot B active. Then in base, you won't hear either drive because their mix is at zero, in morph you'll always hear the B drive, but will only hear the C drive when you switch it on AND are in morph. If you morph back to base state, you'll go directly to clean, regardless of whether C is active, because it, and the B drive's mix are at 0%. Conversely if you have a set of drives in which you want to use the later drive in slot C for rhythm and push it with a drive in slot B for lead, just assign slot B to its own switch, and leave slot C active.
A Similar set up works if you have three drive effects. Maybe for clean you'd like to have a very light drive effect to just color a little, but don't want this on when either of your main drives are on. Just put this light drive in A or D and morph it from 100 to 0. Then it will effectively turn off in morph state when your other drives morph on, only one of which can be heard at once. (Obviously if you want this light drive to stay on all the time, just put it in the slot you want and leave it on and don't morph it. )
Since your drives are only heard in morph state, you could also opt to morph the amp's gain up as well, if you'd like some mix of your amp's gain going up when you're drives are effectively on. Now morphing will increase your amp's gain AND turns the mix of your drives up. Similarly, I've found that I often like the sound of more amp gain for medium gain, but like a drive pedal to help with lead (rather than just upping the amps gain even more than I like for rhythm). In this case, you could have just one drive pedal, say in slot C on its own footswitch. Morph that from 0 to 100% and morph the amp gain from a lower setting to higher setting you want for rhythm/medium gain. Now in base state you hear just the amp at its lower gain stage, whether the C drive is active or not. When you morph, you'll hear the increased amp gain if slot C is toggled off. If slot C is toggled on you'll hear the amp with increased gain AND the slot C drive for lead.
With any of these setups, you could also assign a noise gate, EQ, and/or a pure boost to toggle on when the Slot C drive is on. Just make sure to morph their settings from effectively off in base to their desired settings in morph state. Otherwise, you'll hear them in base state if the are toggled on. In other words, you'd need to set them to sound like they are off in base state, just like you do with your drives set to 0% mix in base state. So for the EQ that means flat settings in base state and however you want it tweaked in morph.