I've thought about it and can't a way except this.
Ask two men if they are men.
You will definately ask the other man if he is (by other I mean the man that lies and tells the truth.)
Since he can do both, I'm sure he'll yes yes. So will the truthteller.
If on says no then you know who the liar is.
If both say yes, then you still know who the liar is.
Ask the liar if the first is the truthteller and the second is the liar (the first and second being the two that aren't the liar obviously.)
If he says yes then it is the other way around. If he says no then you are right.
Again, this is assuming that the man that can choose to tell the truth aor a lie will choose to tell teh truth and say he is a man. If he doesn't, then this could work, if you ask the right people. But, asking the right ones would be by chance and would not be reproducably effective.