Yes! A lot of people do it in the Netherlands! The rescues that are around here advice everyone to take their clipped birds outside on a buggy, so there are whole walks of people with these things, you can do really Nice things with those buggies! I know Some people do use a harness while the birds are on the buggy so that should be possible as well
If you Google: 'papegaaienbuggy' you Will get pictures of examples