When will the next batch with the fixed issues come in?
After everything is where you feel you want it, why not open the flood gates? Inform them that it's a pre-order and use the cash flow to purchase in bulk. This angle avoids getting others involved.
You can get items from China (or the UK) to the USA pretty fast if you're willing to pay for expedited shipping. All of which may look better on you if you overshoot the ETA and they get items in faster than anticipated.
Is this your only option? No, but it turns customers into buyers real quick.
If you don't have enough cash flow upfront you could try and work out a deal with the guy to have a less buy-in. Even if that means a reduction in your WD structure. You already pushed one direct sale to him directly, use that towards your barter. What about different payment terms?