Thompson speedtouch 510 forwarding a range of ports??

I need to config. my speedtouch to forward a range of ports to an inside address. Is it possible to configure a NAT entrie for an inside and outside address for a range of ports , let's say 2000-50000. I need this because I have 2 FTP servers behind this firewall, one uses the standard ports 21(controll) 20(data). But for the other FTP server I can't set the port for data connections, but I can set a range of ports for passive mode. The ftp server prog. is GeneFTpSrv ver. 3.0.0 (build

Thank you.