Purge it or crack the line open with a wrench.
Use a wot switch. If for some reason you don't want to spray right off the line, you can keep the system unarmed and then arm it when you are ready to spray.
Use your tuner to pull timing during shifts. A window switch isn't a bad idea though. The problem with them is when the nitrous kicks back in, it's probably just as hard on the trans as it would be shifting with nitrous.
And x2 on a bottle heater. You will never have any consistency without one otherwise.