Changing Zero Price Action Currency

If I activate the "Zero price action" product option, then the customer can enter his own price except that cs-cart expect this price to be in the primary currency which is confusing to my customers.

How can it be changed to whatever the product currency is displayed in - the currency that the customer selected?

(MV UniTheme if it matters)

Additional code changes are required to do it. It is required to recalculate entered price during adding item to cart