There's no way to do this with standard FTP, but you may be able to use FTPS - assuming that the site you are trying to connect to supports it. Basically, you can think of FTPs as being the FTP equivalent of HTTPS; in other words it uses SSL for file transfer.
There's a demonstration of doing this
here[
^] on Code Project.
You can find more information about FTPS
here[
^].