The more pictures I see from various angles, I am starting to come to the conclusion that NOT theming the BBB was the right decision (and may have been more of a conscious decision and not simply cost cutting).
Once the decision was made to build this ride in this location, there is no theming that could have been incorporated into the building that would not have distracted from SSE. If you put Tower of Terror next to SSE, it would draw the eye away and compete for attention. A space age / futuristic looking building would do the same thing. Why compete with the park icon. You can't hide a building that big with trees.
So, the best way to hide a large building is to put it out in the open. Driving to WDW or though any large city, we see warehouses and large industrial buildings all of the time. Power plants, water towers, utility poles, and other infrastructure. We have been conditioned to no longer notice these items.
When arriving at the park, the BBB sits off to the side. Most people will not realize it is part of EPCOT and their minds will dismiss it. Once you come into view of SEE, that is what will draw your attention. This large shinny golf ball, THAT is EPCOT. While you will be able to see the building from within the park, it will appear as if it is an industrial warehouse outside of the park. For most people, our minds will ignore it because that is what we are conditioned to do. The more that is done to disguise the building, the more it will stand out.
I think we all agree that it would have been better to build a ride that would not create a visual intrusion. But now that it is there, not hiding it might end up being the best (least objectionable) decision.