executing a binary out of a xpi

Hi,

i have a xpi plugin which uses the old XPInstall install.js engine, thus it
is not working in FF3 or in Vista generally (but who cares Vista!?!).

The content of the old xpi is:

META_INF\
    manifest.mf
    zigbert.rsa
    zigbert.sf
ampx.exe
ampx.ini
install.js

The install.js extracts ampx.exe and ampx.ini into temp directory, then it
executes ampx.exe which then copies some files into c:\program files\common
files\Nullsoft\ActiveX\2.6\ and a dll and xpt into c:\program files\mozilla
firefox\plugins\ - dont care about the ActiveX since its just a name of a
directory :)

I already asked in the different channels on freenode and mozilla but i was
told this is the best place to ask.

How do i create a working xpi plugin which does the same as the old
install.js did? I could provide the ampx.exe as direct download but i'm
looking for an automated way of installation. there is also a mime-type
available.

Thank you!