If I understand you need to know two things:
1) When you're at idle
2) When you're above a certain RPM
(2) Can be done with a nitrous window switch. It connects when RPM is greater than some amount.
(1) Can be done with either a mechancial WOT switch set up at idle rather than WOT, or a TPS window switch.
The TPS Window switch (like part # NX 19859) monitors the 0-5V signal coming from the TPS and and then connects when the TPS is above or below a certain value. Your worst case here is that it works backwards from what you want (connects at idle and you want connected at NOT idle) and then you could use a relay to NOT the signal, but I'd check the manual for the switch.
So the WHITE wire from the NX switch goes to the TPS wire on the throttle body. Grey to RPM.
Then you go in and set where your RPM windows are and what to do when you hit them as per the manual here:
http://www.nitrousexpress.com/oldweb...ndowswitch.pdf
It's -possible- you can do the whole thing with just this switch and a relay, but I haven't thought it through that far!