I'll echo what other have said - I would only drop them off in St. Thomas if you/the rest of the crew want to spend some time in the USVI. Otherwise you'll spend a lot of time clearing the boat and entire crew out of the BVIs, into the USVIs and then back into the BVIs. Probably not worth it unless you want to spend at least a couple days in the USVIs. The ferry from Jost or Tortola would be far easier and faster for all involved versus taking the boat over.

However, if you do want to check out the USVI a night or two at St. John might be nice. And if you are a marina person Yacht Haven Grande in Charlotte Amalie is in a good location to drop your guest off and enjoy some of what St. Thomas has to offer. Christmas Cove is really nice as well for a night and you can get a great pizza from Pizza Pi there as well.