Is there any way to build an Apex Trigger/Class using CurrencyISOCode in a multi-currency org, such that it can be packaged for AppExchange but the currencyISOCode will be ignored in a non-multi-currency org where that field is not available?

I guess it will need some sort of dynamic Apex capabilities to determine the schema and behave accordingly.

Presently, it seems that Multi-currency becomes a pre-requisite for installing the package. Presumably this would mean two packages - one for multi-currency and one without - and ultimately two appexchange listings?