change currency

[mtuckerb]

I created an initialiser and put this line in it
ActiveMerchant::Billing::StripeGateway.default_currency = 'AUD'

but my piggyback payments are failing and the stripe logs say that the Parsed Request POST Body ==
{
amount: "110"
card: tok_103KAQ2Rk1i9iyNwylAD97b6
currency: "usd"
}

How do I set piggybak_stripe to respect my currency choice?
-=Tucker