No? It is not possible 
Yes, it is possible 
There are several solutions, but without using variations.
I propose here simplified methods to understand the principle, but they can easily be improved with a few additional manipulations and especially with scripts.
Method 1: a volume widget for each synth, but invert the curve on one of the two, then group the 2;
an expression pedal mapped to any widget to vary the volume of the group.
The rest is simple and quick to implement: you duplicate the rackspace by putting preset n°2 of the first rackspace into n°1 of the second rackspace, and so on. It’s very basic, but it works.
Method 2: same principle, but use a scriptlet to automate morphing launched by a switch or footswitch at variable speed.
See the method created by @David-san: X-fader - crossfade two volume parameters