simple collision detection

So I want to implement a basic kind of collision detection but I don't want to use the built in Collision detection. I Don't want physics interaction as far as objects knocking around and looking realistic. It's part of an editor program and the purpose is to make sure no part of an object crosses a plane.

I initially tried simply checking each vertice in the object to see if it had crossed the plane and if so moving the object in the direction of the planes normal to kick it back the distance from the plane to the vertice.

The problem is the object exists centered on the crosshair.

When you pushed it past the plane it would get kicked out, then since it was out the next cycle trying to exist at the point of the crosshair would kick it back in. Basically it would just jump back and forth really really fast. It actually looked in the game like it existed at the crosshair and never moved because it crossed back so fast.

So I figured the next best solution would be to create a copy of the gameobject and I guess spawn an invisible one there, test if that one is past it and if so move the actual object to that objects modified position? It seems really intensive though to have to copy a game object everytime and was wondering if someone had some other way this could be done? Maybe roughly how its done actually?