Give them discounts for using bitcoins would be my suggestion.
Only thing is, what is in it for the merchants to do this? They accepted
BTC as a payment method, because it's cheaper than the other options, like debit cards and credit cards. Now all of this profit from the lower transaction cost is absorbed, in giving discounts for people who use this as their preferred payment method.
Only option in my opinion, is to give discount in the first few months, until enough people were exposed to this and adoption of
BTC increased.
If DELL did this, they would have seen explosive sales figures.