Have a look at
http://www.mummachummas.co.uk/gtir/BoostControls.gif
Unplug the 2 pipes (marked 6 and 8 ) from the standard Boost Control Solenoid and seal them up by sticking a bolt into each one and taping up (or any other way you see fit!).
You then want to fit your bleed valve in line with the pipe marked 7 (from the 3 way connector to the actuator). So unplug the pipe from the actuator and plug it to one side of the bleed valve then run another pipe from the other side of the bleed valve to the actuator. The 3rd connection (bottom) on the bleed valve does not be connected to anything - but you could connect it to pipe marked 8 to return the vented boost pressure to the air intake. Most people don't bother with this though.
Then adjust your bleed valve to give your desired boost level.
You have fitted an aftermarket boost gauge haven't you ?! The standard one in the centre console will be useless if you are raising the boost at all as it will just go straight off the top of the scale.
Cheers
GeeTee 8)