Can I restrict a product so that a customer can only buy it with a code?

I have a site where a customer asked me if I could hold a jacket for him, and he would pay later. If I disable the item so no one else can buy it, he will not be able to buy it either. Is there a way to have him add the item to his cart so it does not show as available, and he can pay later? Or assign a coupon that will unlock the item or something similar?

Quick & dirty method:

Make a new category name it (for instance) On Hold

Move the item to that category.

Navigate to the item in your store. Copy the URL to that product.

Now in the admin turn off the category (click the green icon so it turns red) and then turn on the product.

Pass the URL to your potential customer.

Now this item is not visible for costumers but can be reached over the direct URL.

It will turn up in a search though... but what are the odds to that?