One of the issues brought up by my friend in discussing Iraq is whether non-violent means can ever really influence intransigent leaders like Saddam Hussein.
There are three places that any tool can be used: internally, externally, and at the boundary of the nation.
In a community of countries that respects national sovereignty, internal operations are generally frowned upon except where conditions are dire (many people are either dying or threatened with death). Non-violent, internal operations such as food distribution, medical services, and education are being provided increasingly by non-governmental organizations (NGOs), which are often under no such constraint.
Non-violent means can be applied externally to alter the economic and physical environment that the errant leader must deal with to acquire resources and dispose of waste. Also of interest to any leader is the possibility of extending power to other countries, and this too can be controlled.
The boundary of the errant nation is where most direct diplomacy (perhaps the most familiar form of non-violent activity) is applied, modulating the inputs and outputs via agreements between the nation's leadership and the rest of the world.
It is fair to say that any one of these regions of operation may not be sufficient to have an effect, but two or more of them may. It would be interesting to do a thorough study of history to determine what correlation exists, if any, between the region(s) of operation where non-violent action has been taken and the successful influence of intransigent leaders.