You can do it. but the reason is why? just for the sound? Putting an external gate on a pair or N1's are not needed (can achieve 400kw in some cases) but they are only need if you are using high power low mounts. Just for arguments sake a pair of 2860's running 25psi obviously you dont need to go external gate but it will help control boost alot better. External gates are usually used for big single turbos or twins making over 500, 600hp + kinda thing..In your case unless you are going for huge horse power you don't need an external gate. If the gate is big enough say 50mm upwards you might get away with 1 but generally if you use 2 turbos you use 2 wastages and you can mount them anywhere you like if you have enough $$$.