Automatic multi currency display on entire catalog.
Run your catalog in a main currency (or a main and alternate) with the customer having the option to turn on an additional currency throughout the Catalog, Cart and Checkout.
This might just be possible, but only with extensive (and expensive) customisation.
This may be somewhat misleading to your customers as the second price is purely informative. Actinic is still working internally in it's home currency and that's what they'll be billed in.