Note that from the outside, free-will is by definition apparently "random". It is a black box not determined by any variables in the greater world. What matters is that the free-will is mine or yours-- that the entity known as to me as myself or to you as yourself should also possess this power of determination which to the outside world appears random.
To witness to the lack of a logical incompatibility with determinism, you can posit a model wherein the will does something like project itself in both time directions in such a way as to keep up the "illusion of determinism". Not that I think such a mechanism is actually in place; this model is just to show there is no logical contradiction, and there could be other models that do the same.