Per the documentation:

CurrencyIsoCode

##Type picklist

##Properties Defaulted on create, Filter, Restricted picklist

##Description Available only for organizations with the multicurrency feature enabled. Contains the ISO code for any currency allowed by the organization.

If the organization has multicurrency and a Pricebook2Id specified on the quote, then the currency value of this field must match the currency of the PricebookEntry objects that are associated with any quote line items it has.

This value is copied from the related Opportunity and can't be changed.

Note that the Currency must be the same as the opportunity, and the PriceBook2Id must also match that currency.

This is all baked in to the standard quote system. You won't be able to subvert multi-currency in the way you'd like.

Per the documentation:

CurrencyIsoCode

Type

picklist

Properties

Defaulted on create, Filter, Restricted picklist

Description

Available only for organizations with the multicurrency feature enabled. Contains the ISO code for any currency allowed by the organization.

If the organization has multicurrency and a Pricebook2Id specified on the quote, then the currency value of this field must match the currency of the PricebookEntry objects that are associated with any quote line items it has.

This value is copied from the related Opportunity and can't be changed.

Note that the Currency must be the same as the opportunity, and the PriceBook2Id must also match that currency.

This is all baked in to the standard quote system. You won't be able to subvert multi-currency in the way you'd like.