You might find some useful information in this topic, where I was asking about pretty much the same thing. And this one.
For VAT reports I found it useful to create a new tax code for USD transactions, so I have VAT 14.5% for all ZWL (base currency) transactions and VAT 14.5% (USD) for all USD transactions. This separates them out in the built-in tax reports, but it shows USD amounts converted to the base currency. Thankfully when I thought of this I didn’t have too many past transactions to change, but if you have hundreds or thousands it could be a real pain to try to implement this retroactively. There might be ways to do a batch update, but I didn’t think I find one when I briefly looked into it.
If you do come up with a good workflow please do update us, as I’m sure others like myself could benefit too.