In case anybody else is interested in doing this, I made the following hackish patch and it seems to work. It requires schroot 1.7.0 or later; I used 1.7.2-3 from experimental, recompiled to run on jessie.
--- sbuild-0.65.2.orig/lib/Sbuild/ChrootSchroot.pm +++ sbuild-0.65.2/lib/Sbuild/ChrootSchroot.pm @@ -125,6 +125,9 @@ sub get_command_internal { '-c', $self->get('Session ID'), '--run-session', @{$self->get_conf('SCHROOT_OPTIONS')}, + '-o', ($user eq 'root' + ? 'unshare.net=false' + : 'unshare.net=true'), '-u', "$user", '-p', '--', @$command); For this to work, you will also need to add a line to the schroot config file (e.g. /etc/schroot/chroot.d/jessie-amd64-sbuild-xyzzy): user-modifiable-keys=unshare.net