Need an example of how to use customTransition (or how to reverse Transition.cupertino-slide-direction)

[xs2bas]

I like to use Transition.cupertino for page transitions, but I want to be able to use it reversed as well: now, the new page slides in from right to left, pushing the old page away, but I also want it sliding in from the left and pushing the old page out to the right.
I think thats not possible with the available transitions, so I was trying to make my own custom transition perhaps, but I cannot find any (working) example of how to use it.

This is what the code looks like now:

GetPage(
        name: Routes.SPLASH_SCREEN,
        page: () => SplashView(),
        binding: SplashScreenBinding(),
        customTransition:  **????????**,
        // transition: Transition.cupertino,
        transitionDuration: Duration(milliseconds: screenTransitionTime)),

Hope someone can help, thanks!

PS I love using GetX :)