A split valve will work, you just have to adjust the VTA port so it only vents a bit of pressure to the outside, open it up and run the car (when warm) up and down the road, if you get a CEL light then adjust the VTA port down a bit and try again until its happy.
Some say 20 to 30% VTA (Vent To Atmosphere) is ok, as long as you don't get a check engine light, your good to go. The venting of boost to atmosphere should be harmless, but the ecu has measured that air once already, and doesnt measure again, it just assumes the same amount is coming back so adjusts fuelling accordingly, if much less arrives then it runs rich and throws a CEL, not damaging like lean running, just annoying.
Since the DV closes on boost and opens when the throttle is released, the engine is winding down each time the DV opens so its fuel requirement is almost zero anyway, and its job is to stop back pressure from a closed throttle (whilst boost is present) causing the turbine to stall or break, so a DV that vents to atmosphere wouldnt break anything, just bugs the emissions control system by causing rich air/fuel ratio on closed throttle wind-down between gears.
Hope this helps! Adjusting your split valve correctly might get the result you want without problems.