Adding detail to photoreal scenery

I've been using the beautiful, freeware Canary Islands scenery by Alberto Sanchez. However, there's a slight issue with disappearing terminal buildings at the airport (GCTS). I've played around with the scenery sliders to no avail, at certain viewing angles the buildings vanish.

My main question is how to go about "detailing" the scenery without altering the terrain mesh? I'm no scenery designer and have no idea as yet what to do. Are there any freeware tools I can use? I suspect it isn't that simple! As well as the markings it would be nice to get a couple more airport buildings in place too.

I did try another freeware GCTS with better markings on top of the photoreal, but it flattened out the airport area and left the horrible cliffs (no surprise there). 

Here's GCTS in the photoreal scenery

Here's GCTS as per google maps

As some of you know, GCTS has large painted gate markings etc. on the floor.

Don't get me wrong - Alberto's scenery makes a HUGE, welcome difference to the stock Canaries in FSX, but I had to ask.

Thanks.