You will have to do surgery on it... by completely removing the section of the barrel where the bipod is attached. Then you will need to replace it with a section of styrene of the same diameter as that section of the barrel... then repaint to match.
When I do surgery on barrels, I try to drill a small hole straight into either section where the connection is made and insert a piece of wire or really thin gauge styrene to help hold it together while the glue dries. Then it adds stability when you're done.