Its not issue if you just add it to valid national currency. In this case it will be more benefiting as people that have currency will be able to use it it this few shops along with national currency and they will seek this shops to use currency they got. And spreaded information about accepting this complementary currency is form of advertising.
Or may be he can just implement a system which allows users to checkout from the store via a exchanger services. For example if Im transacting from USA country but buying stuff on Chinese site then I have to pay obviously in yen. So I find an option called PayPal which allows me to do the transaction in my own currency by converting the stated amount of yen. This type of system can be put in place so that user will come with their credit/debit card and just pay the amount equivalent to bitcoin. The buyer pays in USD or their own currency and seller gets paid into bitcoin with small amount of fees for transaction. I think that would be most easy stuff and good idea.
