Disable moving of image files

Hi all!
I have a question regarding features: I use multiple seperate wordpress installations (five or six) which share one uploads folder (symlink). This is essential and cannot be changed unfortunately.
What I need is:

1. Site 1 uploads image using wordpress. It goes to (say) uploads/2016/08
2. Site 2 runs MediaFromFTP cronjob, registers file and doesn’t move it

Which site does what needs to be interchangeable – so for example I would upload an image in the second instance and it would get registered in the first instance, but not moved.

What is currently happening is:

1. Site 1 uploads image correctly (goes to uploads/2016/08 – this structure must be kept)
2. Site 2 scans image and moves it to uploads/2016/10
3. Image cannot be reached on site 1 anymore as the file gets moved by site 2

• There are about six different instances that need to keep their media synched.
• I don’t want to duplicate image files
• I don’t want the image to be moved (added bonus: don’t move UNLESS they are in uploads/media-from-ftp, but that’s not too critical yet)
• I am aware of the “Organize my uploads into month-…” switch but it doesn’t help as it also changes the wordpress setting for this.
• Optimally I would like to keep the plugin as-is, but if necessary I am prepared to modify the code

Are there any ideas as to how this could be achieved using this plugin.

Also, how could I possibly get some EXIF-strings to be saved not as image metadata but in post_excerpt and post_content?

Thanks so much!