Yes, I have. In a lightly padded ring sling, or better stille, in a non-padded ring sling. The first I had was a Marsupial Mother (scottish made and only has lightly padded rails) and my favourite are zolowear slings (totally unpadded). The baby feeds in the cradle position. That said, I have seen older babies (much older) feeding upright on mums front in an abc style carrier. Ihave not done it though.