Lano,
That setting needs to point to an executable without any arguments.
If you can't inject the right arguments elsewhere (eg, ssh config, other Xfer commands), then I'd recommend making a short shell script, eg, /usr/local/bin/backuppc_sshpass that executes the command with the arguments you want. Then set $Conf{SshPath} to /usr/local/bin/backuppc_sshpass.
Craig