Work on a key word - I use "Busy" or "Get busy" - every time you let the pup out to pee say it. Say it again in a really excited, happy voice as the pup actually pees, "Good boy, busy boy." When he has finished give a quick fuss, stand up and repeat, "Get busy."
Wait - start this on a weekend when you are not in a rush to get to work - until the dog actually does poo and then repeat the praise. When he has finished and is on his way back to you keep saying what a good boy he is to be busy and have a treat ready as he reaches you. Lots of fuss and high happy voice. He is only allowed in after BOTH functions have been completed.
On the first work day let him out ten minutes earlier than usual to make sure the pattern isn't upset - keep it up.
Remember it is unlikely that he will need to poo every time he pees - but as it is a consistent problem in the mornings it is fair to follow this plan for the first outing of the day.