Essentially you can't. At least with unbundling at the VDSL level. ADSL uses different frequencies so it's not a show stopper. With the Openreach rollout there are not other VDSL street cabinets (not much possibility of them appearing) so vectoring should be work. To what extent it will be sub-optimal with ADSL on other pairs in the same bundle, I don't know but maybe that's why there are a lot of tests.