Would somthing like this work. My idea is to run 2 wastegates off of the up pipes. A 50mm to feed the atmosphere turbo and a 40mm to keep overall backpressure in check. Also I was thinking if I keep the pipes divided until the gate I won't defeat the purpose of the divided housing on my high pressure turbo. I hope the attached drawing helps. The placement of the gates is not actual I would like to have them in between the HP turbo and firewall.