I think your question is wrong. You are asking what the best approach to influence your friend is, when there are more philosophical questions you could ask.

• Is there a moral justification to involve yourself in the private lives of others

• is the motive to reduce suffering this way effective

• to what extend is it justified to manipulate instead of arguing with reason

Then the question you ask it what technique to use to influence the behavior. psychological constellations, underlying psychological causes for behavior are unique to a situation. To influence behavior successfully you have to first identify the situation and then dynamically apply an element from any of the 3 options you list when and as long as it is effective. This is a question of psychology and interpersonal skill. Not quite a philosophical question. To assume there is a universally valid model of man that you can apply equally to all individuals to influence them does not exist.

The problem of how to solve such a problem can be solved practically and philosophy can help in such an endeavor.

The only theoretical answer would be to teach psychology. It would be a long and complex answer.