Absolutely, you could do this. One way is to situate the bog garden alongside the pond, to keep all the water features like pumps, liners and plants together for ease of care and maintenance, as well as for sharing water. When building the pond, build the bog garden at the same time and make use of any liner pieces not used in the pond. Allow water from the pond to run into the bog garden but don't let the bog garden affect the pond or it may result in a buildup of too many nutrients.