You can log a Enhancement something like Allow user to Grant permission on sub-folder via Ev search.
So if you get enought votes on ur idea , it might be taken as a enhancement for the future release.
Unforunately what i said in the first post is the reason "I don't think it is possible as normally we add NTFS permission on the folder which will get sync with the FSA archive, but in your case we don't have folder on the filer server.."
Because permissions are sync using the FSA task..
Question : Does the File Server itself doesn't exsists anymore or we just don't have the Subfolder ??
If its just the folder then you may use FSAutility to restore the subfolder.. but if its an issue with the entire volume , then i would suggest to open a case with Support and see if they have any other answer.