After studying the workaround I can now deploy a file to my sourceforge directory. Now I don’t need to upload the file manually with konqueror’s fish protocol.

Just copy the jsch jar version 0.1.29 (!) to ANT_HOME/lib and use the following ant target.

    <target name="deploy-all" description="deploys timefinder for users and developers" depends="-init-deploy">
        <zip basedir="${basedir}/.."
             destfile="${release.file}"
             compress="true"            
             casesensitive="true"
             duplicate="fail"
             whenempty="fail">
            <patternset refid="pkg-all"/>
        </zip>
        <scp file="${release.file}" todir="${username}:${password}@frs.sourceforge.net:uploads/" />
    </target>      

Now invoke ant via:
ant deploy-all -Dusername=yourusername -Dpassword=yourpassword
Please keep in mind that this is not so secure, because other user could see the password with the unix command ps. See the security notice here.