pingit

Got BTSync running on a server, where we now and the drop work files, i then use BTSync on a NAS to just backup the work files, but the space on the server is limited, but when a file is deleted on the main server its deleted on the NAS to, is there a way to avoide this habbit? i just want it to send the new file, not delete when its removed from the server, aint there someway of doing this?