Sorry if I'm missing something.

I have no problem at all generating an itinerary with the calculator such as:

OTP-xMUC-IAD-xNRT-SIN-DAC-xBKK-xVIE-OTP

Whether or not it works for your timing or preferences of course is a different matter.

You will have to make a stopover >24 hrs in a third city to comply with the rules, and you will have to make sure you are not trying to do it all in less than the minimum time.