Finding an inexpensive long stopover "anywhere"

This is not the same as what is the most advanced flight search engine besides Azuon and Matrix? but I would hope an engine "advanced" enough for that one would satisfy this one as well.

The scenario is that one is near XXX and wants to be near YYY by date Z but has no plans for the time in between.

There are search engines that allow an origin and/or destination to be a huge list of places, and one that even allows the word "anywhere."

But as far as I can tell, Kayak, Adioso, Momondo, Skyscanner, & Azuon do not allow "anywhere" as the middle of a multi-city flight. Matrix allows a list, but can't handle very big lists and doesn't have low-cost airlines.

I understand the arguments about computational complexity, but I spent several years doing complex queries on huge databases and it's not as bad as some questions here make it sound.

Currently, one approach I've figured out is to do two searches with Azuon, put both result sets into a database and then join the table to itself. That is not entirely satisfactory, because (for example) it won't find options like XXX to DFW then DAL to YYY.

Another is to manually (and tediously) look for matches in the two searches.

And I had forgotten about this method. But even that won't find everything.

Some engines will find stopovers but won't find very many, and won't show long ones.

I suspect I could do it with one of the expensive tools from OAG, but apparently they found some reason to not honor their offer of a free trial.