Plugin installed via xpi stays packed as xpi on Firefox 4.0

Can somebody give me a hint how to prevent the installation of a plugin
in compressed form?

See https://bugzilla.mozilla.org/show_bug.cgi?id=648510

I have a plugin, packed as xpi, and want to have it installed in
extracted form, just like old firefox version always used to do
(including early 4.0 betas).

Now it just puts the xpi into the profile/extensions directory, and of
course the DLL inside the xpi does not work well in that form (nor won't
find any needed DLLs installed along with it).

I suppose I am just missing some install.rdf keyword?

Thanks,

Martin