ftp server that can block files??

hy people!, the thing is i have an AIX box that downloads things from a ftp and another program that moves everything that's in the directory to another FS the thing is that in aix if you try to cp a file that is in use it says resource is busy but now im migrating the program to suse linux and i find this problem: even if the download hasnt finished the cp or mv starts and my file gets copied or moved in a corrupt state, thats why i was looking for a ftp server that blocked the files until the download has finished . and the prob is i cant change the program to put in a scrip it has to stay as it is!. Help!!