Possible Clues:

• In passing, while we're on the subject
• Incidentally, it's beside the road
• Incidentally, it's a Red Hot Chili Peppers release
• Parenthetically
• At the roadside - incidentally
• Incidentally, it's on the roadside
• You may see milestones here, incidentally
• Purchase residue from cheesemaking, say, in passing
• Article exploring little known area of knowledge incidentally
• 'Oh, meant to say . . . '