Upvote:1
Simply look for the full trip on any site ie. with your preferred starting and end points. The results will give you a clue of the paths flight companies take to reach your destination and therefore what cities will be feasible as stopovers.
Once you see something you like, then use a multi-city booking to include that city, with a day or so in between departures. If it's all with the same airline with daily flights, your costs will be roughly the same as the single flight.
Upvote:2
Try JetPuzzle extension for Chrome. It really does well.
You can try to put any two points and it will list you a huge amount of options including those with literally "anywhere" legs. And making things even smoother, it proposes you variants with arbitrary number of stopovers.