I would say, since there is no reality as "ego", it's pointless to debate whether there is free-will or not, as all are conditioned mental processes.
There is the mind - which conditions the kamma processes of a stream, and there is the path/fruition - which leads to unconditionality after it's attained. One will choose Nibbana over ego-existence, and this is a choice of free-will - not, it's just "realization". Once a small child realizes that fire burns, he won't touch it ever again. This means that, there is ignorance and there is wisdom. And it's all about seeking and realizing. But for that seeking to arise, one needs to be already free from certain types of defilements and states, which is unfortunately, dependent upon kamma. It's the reason why a Buddha is a Buddha, and not some other person. His kamma, allows him to be the Buddha. Dependent origination covers abouts anything - except Nibbana. When one enters Nibbana (well, actually there is no one entering it, because it reality, there is no ego-entity) it's the end of every mental concept, so you can't be talking about dependency or conditionality any more.