building unix installer outside normal tree

I'm trying to build a installer for Linux, following 
http://www.mozilla.org/build/distribution.html

I'm building outside the normal tree:
mk_add_options MOZ_OBJDIR=@TOPSRCDIR@/obj-@CONFIG_GUESS@
so the build tree is in mozilla/obj-i686-pc-linux-gnu

I can package the build as a tarball fine, since 
mozilla/obj-i686-pc-linux-gnu/xpinstall/packager contains a Makefile 
that does that.

But trying to build an installer by running perl deliver.pl in 
mozilla/xpinstall/packager/unix/ fails:
[root@scir unix]# perl deliver.pl
--- deliver.pl: couldn't cp cause 
/share/mozilla/src/mozilla/xpinstall/wizard/unix/src2/mozilla-installer-bin 
doesn't exist: No such file or directory at deliver.pl line 180.

Is it possible to do this with a build in a subdirectory or am I correct 
in guessing that these tools assume the build is in the standard location?

Regards
David