For some reason I lost part of my post about a fix! All sorts of owner-derived variations have been tried, here's an easy one. Remove the old catch-can and breather pipes and seal up the breather pipe unions at the back of the timing chest and the primary chain case cover. Take the larger diameter breather hose with the 90 degree bend and fit the short end over the oil tank breather connection, run the rest over the rear chain by the gearbox sprocket and trim to length. Salvage the short "duck bill" breather valve from the catch can and fix this to the end of the shortened breather hose with a bit of 12mm O/D tube and a couple of clips.
Now if you ride with this all should be well all the time you don't thrash the bike or overfill the oil tank, otherwise you will have some more cleaning to do. You could also use your own catch bottle and a longer piece of hose if you like to give the bike a bit more welly, just make sure your hose run has no dips for the mayo to collect in and cause a blockage.
A.