Hi, I dunno if this can help but:
$ cat /usr/portage/x11-libs/gtk-sharp/gtk-sharp-0.15.ebuild |grep DESTDIR
for i in $(find . -iname Makefile); do cp $i ${i}.orig; sed -e "s:${DESTDIR}/usr:${D}/usr:" -e "s:${D} /usr/bin:${DESTDIR}/usr/bin:" < $i.orig > $i; done
$ cat /usr/portage/x11-libs/gtk ...