Object aways visible

Is there a way to make object visible through another? like visible through walls?

Like in Object Tab >> Display >> X-Ray ?
i think you would have to modify the source
to chage the object render draw order
that would be great. Viewport feature frustratingly not present in the GE

Edit:
and there is the obscure Z offset in Material Tab >> Options
that you can give it a high positive number (in this case)
but its per fragment not per object and you may run into other problems.

What if you did some magic with overlay scenes and a dash of python?

Yes. Copy cameras location and rotation. like in this topic…

This way the object will be visible through all objects in scene, right?

Sim.
yes like any overley scene will.