A law of Reason is an imperative or instruction to do or believe something.

But imperatives require an imperator, instructions an instructor. And only a mind can instruct or issue a command. Thus this premise is true:

1. If there are laws of Reason, then there is a mind whose laws they are

It is also not open to reasonable doubt that there are laws of Reason. For if you think there are not, then either you think there is a reason to think there are not - in which case you think there are, for a 'reason to believe' something is an instruction of Reason - or you think there is no reason to think there are laws of Reason yet disbelieve in them anyway, in which case you are irrational. Thus, this premise is true beyond a reasonable doubt too:

2. There are laws of Reason

From which it follows:

3. Therefore, there is a mind whose laws are the laws of Reason

The mind whose instructions and commands constitute the laws of Reason would not be bound by those laws, as they have the power over their content. A mind that is not bound by the laws of Reason is a mind that can do anything at all. Thus, this premise is true:

4. The mind whose laws are the laws of Reason is omnipotent

The mind whose instructions and commands constitute the laws of Reason will also have power over all knowledge, for whether a belief qualifies as known or not is constitutively determined by whether there is a reason to believe it - and that's precisely what this mind determines. Thus:

5. The mind whose laws are the laws of Reason is omniscient

Finally, moral laws are simply a subset of the laws of Reason (the moral law is, as Kant rightly noted, an imperative of Reason). And so the mind whose instructions and commands constitute the laws of Reason will be a mind who determines what's right and wrong, good and bad. As the mind is omnipotent, the mind can reasonably be expected to approve of how he is, for if he were dissatisfied with any aspect of himself, he has the power to change it. And if this mind fully approves of himself, then this mind is fully morally good, for that is just what being morally good consists of being. Thus, this premise is also true beyond all reasonable doubt:

6. The mind whose laws are the laws of Reason is omnibenevolent.

It is a conceptual truth that a mind who exists and is omnipotent, omniscient and omnibenevolent 'is' God. Thus:

7. If there exists a mind who is omnipotent, omniscient, and omnibenevolent, then God exists

From which it follows:

8. Therefore, God exists.

There we go: a proof of God.