Usually, subcontracting on the supplier perspective (managing customer stock), is quite simple. This is very similar to a normal manufacturing process but some of the stock you will use are not your own. So the easiest solution is to manage dedicated product codes for the customer stock and to value them with a standard cost at zero.

If i'm the subcontractor, would I just create a sales order and then generate a back-to-back work order from there? 

It seems a good idea. The product(s) to use in your production process (as subcontractor) will be identify as component manage in stock. The only change compare to normal manufacturing is you don't own some of the raw material (and you don't pay for it) that your customer will provide to you.  So to avoid adding this stock in your stock value, you can simply set a standard cost at zero. You can use direct supplier receipt to enter this stock where the supplier in that case will be your customer.  

I hope it makes sense.

It seems a good idea. The product(s) to use in your production process (as subcontractor) will be identify as component manage in stock. The only change compare to normal manufacturing is you don't own some of the raw material (and you don't pay for it) that your customer will provide to you.  So to avoid adding this stock in your stock value, you can simply set a standard cost at zero. You can use direct supplier receipt to enter this stock where the supplier in that case will be your customer.  

I hope it makes sense.