Normally the fuel cut is enabled on the overun, but on your "play" map just disable it, so the injectors still fire, I have a 10mm hole in my lambda bung to let air in, and the bangs when hitting the hard cut 4500rpm are ace, the soft cut I set at 4200rpm.
I tapped a thread in the hole so that I can insert a bolt for the mot, ie so there's no leak to fail the car.
Best of luck with it anyway.
tabetha