My suggestion is to not make a trip out of a Cambio stop. What I would do would be to plan in advance when I needed to get a "charge" of money [i.e. go to a Cambio] and work that stop into a restaurant stop or a HiLo Market stop etc. Any driver will stop and wait for you to go into a Cambio before taking you to your real destination.
That way you are not out walking the streets or the beach with an excessive amount of money. In fact, I would go into the taxi without money knowing I was picking some up at the Cambio (if you go the Traveler Check route as you previously stated).
Peace and Guidance.