Follow these steps.
1. Initialize your iTwin with a name say "John Doe"
2. Seperate the two halves of the iTwin device.
3. Open the Dropbox folder.You will find a folder by name 'iTwin SecureBox - John Doe'. Share this folder using Dropbox with your friend(using the email address connected to his Dropbox account).
4. Give your friend the one half of your iTwin device.
5. When your friend inserts his half of the iTwin into his computer on which his Dropbox account is open and running, he will be able to see the files you put in the SecureBox for him.
6. You can use both Remote File Access and SecureBox with your friend.
Please contact email@example.com if you need further assistance or clarifications.