I see two options here:
1. As described in my tutorial mentioned above. Basically you show loading screen at the end of the first layout and you hide it once everything is loaded/stable on the second layout. It doesn't speed up the loading process but at least you get rid of that "freeze" feeling.
2. C2 engine clears the memory while switching between layouts, but it keeps the objects which are used both in the layout you are now and the one you are switching to. So basically all common objects remain in the memory and there is no need for the engine to reload them. You can use this fact and load the assets you need in the next layout just before switching to another layout (or during gameplay... up to you).
I think you don't need to place the second layout assets in your first layout. Never tried it myself but simply spawning those objects from the code should do the job.
There's another trick here. Keep in mind that C2 engine does not load objects which are outside visible area, so spawning an object at position -9999, -9999 won't work. Also invisible objects are not being rendered. So you need to do some kind of dirty trick like:
a) spawn object at any position
b) set it's opacity to 1 (almost invisible)
c) set it's position to overlap visible area (it doesn't have to be the middle of the screen, it can be partially visible somewhere in the corner)
d) wait 0.017s (that's the duration of 1 tick), not sure if this's gonna be needed but I believe it will to force the engine to load/render the asset
e) set it's position somewere far away
Might look complex but if you prepare good generic code then it's just a matter to setup some lines in event sheet for each layout.