Type the letter E (to enable Envelope Tool), right-click on the waveform, go to Envelopes, Create Track Envelope, Volume (or anything else you prefer). You will now see a horizontal line across the waveform. This is your 'rubber band'. Double-click on the line to create a point, which you can move all around. This goes down to the sample level, so you can get very accurate volume/pan/effect envelopes. This is nondestructive as it actually instructs the real-time faders to move according to the line's position - basically, the volume will follow the level of the line.