ftp GET and partial files

I have a folder where large files are constantly copied to, from a 'master'
folder.  There are also files that are created dynamically on this folder.
Another workstation connects to this folder via FTP and downloads these
files manually.

Is there a realiable way to tell the FTP client not to copy a file that is
currently still in the process of being copied or created?

Thanks.

Ray Mond