Grinding works and is easy. If I can do it...anyone can !
Wages in mainland China for jobs like postmen are sickeningly low so postage is cheap, slow and unreliable. Most people use couriers to do the cross-border trade because there is a huge volume and it is same day, not 3 weeks, and doesn't cost that much - a fraction of what UPS and FedEx charge. Unfortunately the Ebay sellers won't use a courier.
I'm not willing to wait another 3 weeks to repeat the same problem, and there aren't any other Ebay sellers who will post to HK that I can try, so I'll just have to get over-sized batteries from a local shop and grind down the boards.
BTW, the alps pot now has some noise on it so if anyone is in the same situation as me, desolder and remove the volume pot before you grind.
Of course, better to get a full supply of the batteries in advance of building the boards.