It would only take a tiny bit of quantum indeterminacy to initiate an event within the neuron activity in your brain to invoke a consciously driven choice. Scale does not matter.
Well, scale probably does matter in the overwhelming majority of cases, but let's play Devil's advocate on this, let's assume there's an instance where a brain is deciding between two options, and it's come down to a 'casting vote' by one neuron. It's almost at the tipping point, and we have one final electron settling from a quantum state into one of two positions which will either mean the neuron's active or it's not.
If that quantum event is random then you've got a tiny, tiny element of a piece of brain activity that isn't deterministic... so it's 'free', but what you've lost is 'will'. You've replaced inevitable consequence of prior events to absolutely independent of anything. I don't see how that benefits your claims.
And I do not think you appreciate that truly random quantum events would never sustain the stability needed at molecular level. Molecular stability requires the probability of specific quantum events to occur at specific times.
Sufficiently large numbers of predominantly deterministic events with a random element - like, say, weather patterns - for sustainable (if sometimes dynamic) patterns of activity, so it's possible.
If human will can have control of some quantum events in our brain, then God's will could have the control over quantum events on a much bigger scale to sustain molecular stability.
Both of those are extremely doubtful 'ifs' though. There is nothing that suggests, outside of Chopra-woo, that human 'will' can control quantum events, and nothing to suggest a god, let alone a will of a god with the capacity to exert that quantum influence without any apparent physical presence or existence at all.
O.