Use the Audio Mixer in Automation (Read Write) mode and do it live.
I suggest you read the help file on this reasonably complicated procedure so you undertsnad it fully.
May even be a vid tutorial on it somewhere.
Thanks for that shooternz. I should have explained I have read the help file and also (unsuccessfully) looked for a video but am still none the wiser, which is why I posted on here hoping someone can give me a quck pointer :-)
With the proper Send settings (Write, Touch, etc., as Craig mentions), you can easily ride the Volume in real-time. I like to add a Numbered Marker to where I want the adjustment to begin, hold, and then end, so that I have several visual clues, besides the aural ones.
I also have found that the default setting for Audio>Minimal Time Thinning Interval places too many Keyframes on the Track, so I have bumped that up in Preferences.
Also remember, the Keyframes added with Audio Mixer are Track Keyframes, and not Clip Keyframes. If you were to remove all Clips, those Keyframes would still be there, and would affect any Clips that you added back.
Here is a more specific example (vid tut) regarding Mixer Automation.
It is for Audition but the principles and controls are pretty much the same in PPRO Mixer Panels.
Worth looking at the entire vid for context but Track Mixing (as opposed to Clip Mixing) starts around 4:30
Ok got it working now. Thanks everyone!
Sorry to jump in on this, I know this has been asked many times and the answer is usually 'no', but are there yet any hardward mixer controllers that Premiere Pro supports? I hate doing this is a mouse!