1) If you look at http://www.jsftoolbox.com/documentation/help/12-TagReference/html/h_outputFormat.html you will find that h:outputFormat has a converter attribute. I can try to use it(But you will have to declare named converter in your faces-config.xml).
2) I guess you can also try to add f:convertNumber as a child of h:outputFormat and see what happens.
h:outputFormat uses MessageFormat.format() for output string. See MessageFormat api documentation for information about how can convert param.