It's actually quite easy to test the stage2 installer, I don't know why I'm so resistant to do it.

• install build dependencies

sudo urpmi /SRPMS/contrib/release/drakx-installer-stage2-10.4.171-1mdv2008.0.src.rpm

• build and install stage2 in /export

cd ~/vc/mandriva/soft/drakx/trunk/perl-install/install
make
make install

• boot stage1 with automatic=method:nfs,network:dhcp,server:dynamo,directory:/export on the kernel command line

• update /export after each pm file modification

sudo make install_pms

• restart installation with Ctrl+Alt+Home after modifications (not really clean)