What app are you using?
In vegas you can right click the track and then select add volume envelope. When you do that, a colored line appears and spans the length of the track. That is the gain envelope. You can zoom into the spot time-wise and amplitude-wise (using CTRL/SHIFT-up/down arrows), then you can add bend points to the volume envelope by double-clicking on the line. Just add a point right before the gain shift happens, and add one more right after the gain shift happens. Then you can just grab the envelope on either side and raise/lower it. You can use this same technique with panning and any automatable plugin too (you could just as easily ride the threshold of a compressor up or down over time this way).