Automatic currency conversion for already existing products/services

Right now, product prices for new subscriptions/products/services are updated, but not prices of those which have been already ordered and are renewing. Thus if I have a client paying in USD with base currency EUR he only ever pays the same USD price, while the USD/EUR ratio changed a lot from last year. Thus I need the possibility for configuring the USD price to re-adjust itself also for running products/services.