Here is one possible solution:

1. Go to airwander.com
2. Click on the "Roundtrip" drop-down menu, and change it to "One Way"
3. In the origin and destination airport boxes type "Addis Ababa - ADD" and "Paris - CDG" (One limitation seems to be that you do need to select a specific airport rather than just "Paris")
4. Enter the departure date (5/8/20)
5. Click the red "+" button and let the website do it's thing for a few seconds.
6. The result is a list of stopover destinations sorted by the amount of money they would add to the non-stopover price (from low to high).
7. To change your desired stopover length, use the -/+ buttons near the upper right-hand corner of the page.
8. If you want to look into specific flights, click on that stopover destination, and click the blue search button.

Looks like the most inexpensive option for the example you gave is a stopover in Rome. Hope that helps!

Here is one possible solution:

1. Go to airwander.com
2. Click on the "Roundtrip" drop-down menu, and change it to "One Way"
3. In the origin and destination airport boxes type "Addis Ababa - ADD" and "Paris - CDG" (One limitation seems to be that you do need to select a specific airport rather than just "Paris")
4. Enter the departure date (5/8/20)
5. Click the red "+" button and let the website do it's thing for a few seconds.
6. The result is a list of stopover destinations sorted by the amount of money they would add to the non-stopover price (from low to high).
7. To change your desired stopover length, use the -/+ buttons near the upper right-hand corner of the page.
8. If you want to look into specific flights, click on that stopover destination, and click the blue search button.

Looks like the most inexpensive option for the example you gave is a stopover in Rome, but for $80 more you could stopover in Casablanca (that's the cheapest African stopover). Hope that helps!