ant: handling jar whose contents have file permissions 000

I am trying to overwrite the default icon of installer JAR crea开发者_开发技巧ted by IzPack, with one from my application:

<jar update="yes"
  jarfile="${pwd}/dist/${release}_installer.jar">
  <zipfileset src="${pwd}/dist/app.jar" includes="com/izforge/izpack/panels/**"/>
  <zipfileset src="${pwd}/dist/app.jar"
      includes="com/xyz/img/logo.png" fullpath="img/JFrameIcon.png"/>
</jar>

This task works in an ordinary JAR file, but the img folder of the installer JAR appears to have 0-0-0 file permissions on it, such that if I extract it (notice no rs or ws):

$ ll
---------- 1 bguiz staff  742 2004-05-29 11:39 JFrameIcon.png

This also means that my ant task above execute, but fails to replace the required file. Is there any way to work around this?

NOTE:

Constrained to using Ant 1.7.1, thus the preserve0permissions attribute of the jar task is unavailable.