Skip the space gray Magic Trackpad 2 with your iMac Pro? Here’s how to fix that

A few weeks ago I purchased a base model iMac Pro in store, so of course it came without a space gray Magic Trackpad 2. In my excitement to get the new machine, I totally forgot about the Magic Trackpad 2, and it didn’t fully dawn on me until later that there was no real way to acquire one from Apple after purchase.
In fact, Apple explicitly states on its website that space gray accessories [including the Magic Trackpad 2] are available only at the time of your iMac Pro purchase. So what&r