There is no option for preloading, you can preload assets into memory, but you cannot have events preload.
Instead of preloading, have the layout start with a non-transparent layer on top of everything. That layer is basically a loading screen, once everything is done generating, set the layer to invisible.
I use a global layer that I fade in on pressing the button, and fade out once everything in the next layout is done. With the fading it looks pretty smooth.
There is also this, but I don´t know if it covers your case. I´ve never used it.
scirra.com/store/construct2-plugins/mmpreloader-layout-preloader-3620