When you say "over", you mean "on top of", right?
I'm not knowledgeable enough on what's possible to answer definitively, but this might require turning off blocking/clipping for the entity, entirely. I'm not sure if there's fine-grained control enough to just allow Spidertron.
I can think of a semi-crazy, creative solution though, where it uses an invisible hollow rectangle, like a perimeter wall, for the blocking/clipping. I think that'd prevent the player from walking on it, but allow Spidertron to walk over it. It might also unfortunately, allow placing entities inside of (on top of) the power plant.
Would that achieve what you're requesting? I'm not sure when I'll have the bandwidth to experiment with it, but we'll see. Sounds fun. :)
