A wire frame render is just a “cell render” this is an option in the effects tab of the render settings menu. Enable edges.
I cannot think of an automated way to render out your nulls.
I would model a look alike of it then with that selected use the transfer tool to place it on the nulls. this will have to be done manually.
-Select object
-Functions:transfer
-In attributes manager drag the null object into the link
/randy