The easiest way to do this is simply automation. As you can see in the picture I provided below, the technique is subtle but very effective.

EDIT: Take advantage of the combinators & mixers. Use a combinator, add a mixer of your choice, then use the reverb unit of your choice and use it as a send effect, then draw in your automation.
-Another great reason to use this trick is to let other synths breathe throughout the track. Too much reverb can lose focus on synths and cause the mix to be dull.
-Please note that you can try whatever automation 'pattern' suits best for the synth you are using (I usually prefer the 'sidechain' effect). Making music should be all about breaking expectations and doing whatever the fuck you want.
Hope this can bring something to your tracks.
-AVENSA