I do this as well, but I don't "lie" (from the perspective of my core values).

I empathetically accept the other person's ethics and decisions. I allow that common connection to genuinely color my tone and physical expressions, which seems to build rapport just as well as actually verbalizing agreement. When I find myself about to verbalize agreement of something I don't actually believe, I consciously pull back. The trick is being able to pull back without losing your empathetic connection.

Anecdotally, I find that I can verbalize disagreement, but as long as I maintain the tone and physical signals of agreement (or 'acceptance', perhaps, but I think 'agreement' is more true) that the other person remains open.