Deltup now has scripts for complete integration with the portage system.  To have deltup automatically download and apply patches when you emerge, you must change your FETCHCOMMAND environment variable to 'efetch ${URI} ${DISTDIR} <optional ftp site>'.  Since the Gentoo mirrors do not currently have patches to download, you should put my ftp site in the place of <optional ftp site>: "ftp://sunsite.dk/projects/deltup/patchfiles".
  There are also several environment variables which change the way deltup functions:
  PACKAGE_FETCHCOMMAND (defaults to using wget),
  PATCH_FETCHCOMMAND (defaults to using PACKAGE_FETCHCOMMAND),
  PATCH_RESUMECOMMAND (defaults to RESUMECOMMAND): you can set these to your preferred download program.  Use the same format as Gentoo's standard FETCH/RESUMECOMMAND.  They default to using wget.
  PACKAGE_PATH : use this if you have other package repositories on your mounted filesystems.  You may specify several, separated by spaces.
  GENTOO_PATCH_MIRRORS : not useful until Gentoo supports deltup, but it will be used to list the mirrors that contain patches.  It defaults to GENTOO_MIRRORS.
  DTULISTDIR : use this if you would prefer deltup not to store its dtu information file in $PORTDIR/profiles.  This location has the special advantage of being cleaned out when you do "emerge sync".