Hi,
We did register at two places since my coworkers kept bugging me about it. On our webpage, under the registry tab, we put a little note :
Because this will be a Destination Wedding, gifts are not necessary. However, we have been getting some requests to register anyway, so we will register at a couple of stores
To be honest, I don't think you should expect your guests to buy you gifts on top of already spending hundreds or thousands of dollars on your trip. That being said, you can always just put out a registry anyway (power of suggestion) and say it is for co-workers.