Thank You all for replying.
In concusion it seems You have to rely on Your own judgment and creativity.
In some polish forum, one atco also send me a link to Aeroperu 603. On wikipedia there is an information that the controller sent a B707 to guide Aeroperu down safely.
Would You (as an ATCO) approve such flight? Would You agree to willfully loose separation for them to see each other? Would You do it if the pilot asked You to?