You can create a Favorite to do this easily, and attach a keystroke to it. All you need to do to create the Favorite is go to Favorites>Start Recording Favorite and then use Ctrl-A to select the entire clip, then turn the HUD wheel down to -96dB. Then stop recording the Favorite and give it a name. Then use Undo to put all the audio back in your file...
Now that may seem slightly crazy, but you'll find that now, if you make a selection of just the audio you want to reduce the level in, and apply your Favorite, it will apply just to that selection. If you look at the edited strokes for it, you'll see that they are 'Relative' and set to 0 and 100%, so apply just to your selection and not the whole clip - which is what you might have thought would happen. If you start creating a Favorite with any selection other than the whole waveform, it will make absolute percentage selections, and the position and length of these will vary according to the file length - just what you don't want.