Maybe it can be solved in another way:

Maybe a flat area could be created to ring around the central shaft. It would allude to the central spike as the shaft we see (which is what I always thought it was). The picture of Luke underneath might have to be modified a bit (showing the conical feature to the right side, while keeping the area Luke is underneath flat), but then again the area he is under is as large as a few city blocks (compare the flat area to the city on the top), so no change would be necessary except for maybe the far off shots of Cloud City to show the flat ring around the lower base.

It would be interesting to see the shots with the Falcon before, during and after they pick up Luke, to see if any of the main shaft or other underside details could be included. Also, is it me or could something be done to the underside to show it extend a lot more into the background (more antennas, with the grid work extending back more, etc)?

I could also see that establishing shot of the main shaft exterior being modified (when Luke first falls out of the garbage door, he looks down and watches debris fall away), such as more skyscraper style pulsing red lights, etc.