Hey Kook,
Can you post a link or screen shot of the fine print stating customs issues? I too blazed through the check and thought having the PSU pre-installed would just make the whole process simpler/smoother.
My guess is that it won't be too big a deal, as all the prior batches have had PSUs so I can't imagine it would be too much of an impediment.
http://store.avalon-asics.com/?product=avalon-asic-unitbelow the price:
without power supply option highly encouraged as it is known to have less problems in customs!