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It would help to know when you are planning to travel. For example between Jan 2 and April 30 2017 the PeruRail 'train' service (The Hiram Bingham) is bimodal with a bus from/to Poroy to/from Ollantaytambo and train from/to there. IncaRail also offers services from Ollantaytambo to Machu Picchu.
Singles are available from both operators.
You may however prefer to return with PeruRail to Urubamba, since from there Moray is only about 40 minutes by road, and then work your own way back to Cuzco from Moray.
Further details here.