An argument against theistic determinism

A pattern of argument against determinism that is worth exploring is not to argue that free will is incompatible with a variety of determinism, but instead to argue that some other feature of our moral life is incompatible that variety of determinism. For instance, the following argument is valid:

1. If theistic determinism holds, then all our character features, histories and choices are entirely determined by God. (Premise)
2. If x's character features, history and the choice to promise p to y, are entirely determined by y, then x's promise of p to y is invalid (and hence non-binding). (Premise)
3. One only validly promises something if one chose to promise it. (Premise)
4. Therefore, if theistic determinism holds, no promises to God are valid (by 1-3).
5. Some promises to God are valid. (Premise)
6. Therefore, theistic determinism is false. (By 4 and 5)

I think one can use (2) in an argument for incompatibilism. You start with (2) and add the premises:

7. If x freely promises to y something permissible, then x's promise is valid.
8. If some free choice can have an ultimate cause outside one, then a freely made promise of something permissible to any person whatsoever can have an ultimate cause outside one.
9. Whether an action is free does not depend on conditions a hundred years before one's conception.

Then, you use a variant of this argument.