how to use pbuilder without .dsc files?

[Shawn Sörbom]

Hi,
I am using pbuilder for the first time and I was wondering:
How does one build a package in pbuilder if they haven't generated .dsc files?
I am trying to build a package on my stable system that has dependencies which 
are only satisfiable in sid. I have not built this particular version yet, so 
there are no .dsc or .changes files. what should I do?
Thanks,
--Shawn