rebuild .src.rpm from .rpm

[Matt]

Hi guys

I'm learning the ins and outs of package building, and have a query the
man page doesn't seem to answer. I have downloaded an .rpm since there
was no .src.rpm provided. I would like to rebuild for my architecture.
Thus, I would like to know if there's a way to generate a .src.rpm from
a .rpm package? Something the opposite of a `rpmbuild --rebuild
pkg.src.rpm`.

TY
-- 
Matt