Instead of click-to-copy, you could do click-to-highlight, so that "right-click > Copy" highlights the text on right-click if it's not initially selected. There is some subtlety in the logic, because it shouldn't interfere when the user manually selects a substring.

For a demo of click-to-highlight, install IPvFoo and use your mouse in the popup window. See the 'selectWholeAddress' function in https://github.com/pmarks-net/ipvfoo/blob/master/src/popup.j...