You mean, I charge or refund the differences because of the rate between ECB and paypal? This rate varies alot (not sure how often it change), its hard to keep track and might end-up under or overpayment while thinking I have setup the right fee for the differences.

Is there an option probably in the paypal plugin to use they paypalx service? In order to use their api, I have to supply api username and password which they can only give to a user with business type account. Maybe you can have this feature included?

I might be able to extract the converted currency value based on that api but I am still thinking what to do in order to reflect the new price for all product displayed.