Option to select subfolders on a NAS as the backup destination

I have a NAS and I want to use it as a backup for my Monument. But since because of the folder structure thats not possible. I can connect to my NAS from my monument and select it as the destination for the backup but it only lets me chose the main folder as the destination of the backup. I would need to chose a subfolder on my NAS as the destination since, since the fist folder that shows up when I connect to my NAS is not the one I can write to.