Upvote:1
Well, look at it a different way, there's no need to 'force' a connection, just book an itinerary with a connection in a city you want.
Be aware though that the airline you want to fly might not offer that connection at all. For example, there is no way to force Lufthansa to connect you in London.
If London is you preferred stopover, look at airlines that hub in the London area such as British Airways, Ryanair or EasyJet.