I figured out a way to get trails/spillover! I used the new ToggleSwitch4 (utility) and assigned 2 sets of effects to the toggleswitch that I can easily bypass. I ran a stereo signal through the other 2 toggleswitch channels that are always on so that there was a constant dry signal going through. Then, I just assigned the footswitches to bypass each of the 2 effects.
So for example, footswitch 1 turns my ambient sound on and off and then footswitch 2 turns my tube screamer on and off. So, it's an amazing setup I've got now - all because of the 4 way toggleswitch! And, I added the toggleswitch to the beginning of the signal chain so that my ambient tails/trails wouldn't be cut off when I bypass the ambient sound! It's amazing!