I dmg'ed and uploaded the original pkg + the file to be replaced here: http://www.multiupload.com/GXQJ46M52C
The modded Flash Player.plugin needs to go into Adobe Flash Player.pkg/Contents/Archive.pax.gz, replacing the existing lzma compressed one. I included the plugin uncompressed so you have a virgin state, to eliminate lzma compression issues.
I really want to learn how to do this. If you can produce a working installer with the files I provided please share the how2 with me!
FYI: the flash player plugin is a mod which works with Firefox 3.6.x, which the current Player from Adobe doesn't. This mod naturally also works with Safari & Chrome as supposed to. More info here. The terminal-based command script there obviously does not work for everybody so I want to go the "original" way.
[EDIT]: the installer also needs to contain flashplayer.xpt (attached)