First, perhaps to state the obvious, that page turn transitions can't be programmatically created -- therefore if your slides are individual scenes then the way to avoid page turning to another scene is to just not have the page turn transition onto the next scene! But I'm guessing that isn't what you had in mind...
If you need to conditionally allow/disallow page turning you could also put a blank element over the scene that has an On Drag action set to it. You could animate or program its display property when you want it to change states. I'd put this as the lowest element on the scene so it doesn't interfere with other element mouse actions.