pull the stop lamp fuse from the drivers kick panel if you want the ECU to not close the throttles when you try and throttle and brake at the same time. This is what everyone who drag races has to do with a Z to get a proper burnout. There are other ways, such as putting a toggle switch on the stop lamp input to the ECU, etc... but the quick easy way is the stop lamp fuse. I believe its the 3rd from the bottom, left column.. Take note, your brake lights will not work with this fuse out!
But I would just pull the trans
