Convert currency when checking out with Paypal

I have a website in Bulgaria and the primary currency is in Leva. I offer Paypal as a payment option. However, Paypal does not accept Bulgarian Leva as a currency. On my website I have a message by the Paypal checkout option which tells the customer to switch to Euro. But, as can be expected, some customers do not change the currency and get rejected at Paypal. Is there a way to automatically change the currency to Euro if they select Paypal Standard checkout? I am using OSCommerce 2.2 RC2.