32-bit to 64-bit

["Mark Allums" <mark@allums.com>]

Can one do this?  Not: Is this easy, but merely: Is this something that is
feasible?

I have a 32-bit system that I would like to migrate into 64-bitness within
the same basic framework, within the same "install".  That is, can I go from

32-bit kernel-arch + 32-bit userland =>
64-bit kernel-arch + 32-bit userland =>
64-bit kernel-arch + 64-bit userland

within Debian Squeeze or Wheezy, or Bodhi Lucid or Precise?  Without a clean
install?

I was thinking that multiarch might help this happen.  

Advice?