That probably cannot be done since the borders are easily accessible from all sides. Both the internal borders of greater Europe and the external borders are practically open as should be clear from the extensive history of uncontrolled migration in the region aside from the brief periods of actual policed walls in a few locations.
But that's what I was saying [writing, rather] - that it cannot be done without a bloodbath. The last known attempts at obliterating cultural identities on European landmass were Katyn forest [a relatively small scale attempt at "surgical change", picking the social leaders and potential leaders only] and - more comprehensively - Holocaust.