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.