Using vanilla kernels with encrypted /

[Tobias]

Hi,

my question is only partly an Ubuntu kernel issue, but hopefully someone 
can point me into the right direction.

I test latest kernel-rcs from kernel.ubuntu.com on my laptop using the 
provided debs. Now, recently, between rc6 and rc7, the config of those 
kernels seems to have changed, which currently prevents me from booting 
the rc7. After the problematic change seems to have been identified, I 
would like to build an rc7-based kernel myself without the problematic 
feature enabled.

Now the problem: When I use the sources from kernel.org with the config 
(e.g. the one of rc6) that comes with the debs from kernel.ubuntu.com 
(or a fresh one), the resulting kernel does not boot because somehow it 
is unable to do the cryptsetup, apparently / is not found.

How can I tell make-kpkg to do the same magic that must take place 
whereever the ubuntu-debs are compiled so that I end up with a working 
kernel?

Thanks in advance,

Tobias