The only way to eliminate iron triangles that could possibly work in our democratic system is to create more interest groups.  If there were more interest groups on more sides of each issue, iron triangles could not form.  Let's say we have an iron triangle in which interest groups that represent banks control financial regulators.  The way to break up such an iron triangle is to also have interest groups that represent depositors and consumers and taxpayers.  These groups would put pressure on Congress and the regulators that would offset the pressure being put on by the banks' interest groups.

In a democratic system, we cannot (and should not) prevent interest groups from having their voices heard.  What we can and should do is to have more groups expressing more points of view so one group cannot form an iron triangle.

What could be done to eliminate iron triangles?

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.