There are a few things that could be done that might eliminate iron triangles, but none of them is likely to be politically acceptable and some would probably be found illegal by the courts.
One thing that could be done would be to prevent an interchange of personnel between the interest groups and the bureaucratic agency. People from an interest group could not go and work in the agency and vice versa. This would help prevent a common set of ideas from coming to exist in the two organizations.
Another thing that could be done would be to prevent the interest group from giving campaign contributions to the members of the relevant Congressional committee. This would prevent the members of Congress from needing members of the interest groups.
These sorts of actions, if possible and legal, would loosen the hold of iron triangles.