Like Bermuda, tax every purchase of foreign currency, even transfers from a BBD to a USD account in the same bank. The banks should collect the tax and send it to central bank every day/week/month.
0.025% tax should be small enough to keep voters happy but large enough to ensure the foreign currency well doesn't run dry. It should cut down a lot of admin and avoidance that you get with specific foreign currency limits.
In order to avoid unnecessary tax on interbank transfers on island, the central bank should work with all domestic banks on a central clearing facility that allows interbank transfers, at least for BBD, without requiring international transfers.
Happy to help set this up. Or at least learn why it is unfeasible and help work on a more feasible option..!
Submitted by N. Taggart