repoman currently ignores PORTAGE_CONFIGROOT, but it should not. Reproducible: Always
This is fixed in git: http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=4abd7ee534a78b78bcec8ebfdcbc023e5ba30bd3
Thanks!
This is fixed in 2.2.0_alpha90, but I'll leave this bug open until it's in an unmasked release.
This is fixed in 2.1.10.50.