Not sure if this helps, but this is how I would do it:
1. Load into MCX.
2. Export "clump" to something that can be read by your 3D program. If GMAX, then 3DS. Not sure about what can get imported into Sketchup. In 3DS format, however, the textures are kept and the mapping is preserved.
-- I'm proceding as if you were using GMAX since this is a mix of Allen's tutorial and Milton Schuppe's (sp?) videos. I'm guessing Sketchup is similar, but the wording may be different for the procedures I'm describing.
3. Load the 3DS object into your design program. You should have the entire "scene" with all the buildings showing.
4. Select the building you want. I'm guessing it's the planars/polygons which then have to be selected then "separated" into another object. Name it what you would like.
5. Delete the other, larger "clump" object so that all you have left is the building you just created with the "separated" polys.
6. Center axis to the new object, then lower to the "ground" level (ususally '0').
7. Exit the axis edit mode then change the X,Y,Z to '0,0,0' so that the object is now at the center/origin of the program. Rotate to match the different "scene" or "world" axis if needed as well at this point.
-- NOTE: The textures should still be mapped as they should be.
8. Export as "mdl" to a working folder. FSX doesn't care since I believe it's just one type of mdl with it, but in FS9 it's either scenery or aircraft. If for FS9, make sure you have the correct version (scenery).
9. Repeat with all the buildings/objects in the "clump" you wish to break up, remembering to center the axis and then center the object to the origin before saving as another "project" file then exporting to "mdl" format.
10. Once done, use Arno's Library Creator to load all the mdl's and make a library for the project. You can also make a "txt" file with all the mdl names using this neat program so you're not searching to see what building is what GUID.
11. You can then use the library to place the objects wherever it is you would like with IS3, EZScenery, etc. You can even use direct XML placing if using the SDK stuff with "bglcomp.exe" as a "drag-and-drop" or bat file.
I haven't had a chance to try this method of MCX-Design Program all the way through, but it seems like that method should work in theory based on Allen's tutorial for aircraft and some of the tutorials I've seen online (like Milton's) for working with GMAX (or any other program, I would think).
Per Allen's tutorial, you just remove or delete what you don't need from a scene. In the aircraft's version, you're working on a TBD from CFS2. When done, you then merge things back together after you work on them.
There's no reason why something similar couldn't be used for scenery creation, but with the obvious changes I mentioned above.
Just a guess, though.
Oh, and it just may take some time, too.
Regards,
Jorge
Miami, FL
PS: Are there any other e-mails or communication methods you know of other than MAIW? Maybe Jon retired from FS?