I may not be understanding your situation completely here, but ill take a quick shot - from what i’m gathering, it sounds like you are needing two different objects to have diverse colliding behavior in regard to a single static object.
The immediate suggestion that comes to mind = Collision Profile’s.
Is this something you have already attempted? If so, would a custom profile make sense?
Otherwise, the only other method that might be of help is to model a new mesh (or mesh’s if it concaves or makes sense to have more than one collision mesh) and create the collision using either UE4’s auto-gen or within your 3d program. Below are the steps to do this if needed and just for reference I will discuss this as the ‘SecondaryMesh’.
→ Import the newly created SecondaryMesh into the engine
→ In the content browser, open the model you want to apply the custom collision to (lets call this ‘PrimaryMesh’)
→ Head back into the content browser screen and open the SecondayMesh
→ I think this will only work with simple collisions, so make sure you can see a green collision poly for your mesh. This is in fact what will be copied over and not an outline or anything in regard to the mesh itself. If needed, modify the collision with the available UE4 tools via ‘collision’ menu at the top.
→ After you are happy with the collision that will ultimately be copied, re-confirm that this mesh is still in fact selected in the content browser, then proceed back to the PrimaryMesh screen
→ Using the ‘Collision’ menu again, you should now see an option at the bottom labelled ‘Copy collision from a static mesh’.
There is a good chance you may not see anything happen - make sure to re-enable the ‘Simple Collision’ view checkbox and this should reactivate the collision objects. If you still do not see it, go into the Wireframe mode and make sure the collision isn’t hiding inside the PrimaryMesh in case there is a size difference. You can adjust the scale and rotation if needed.
Hopefully this helps.