It can be done, but BBS doesn’t support it.

For reference, in case the link above breaks:

Instructions

To prepare your Yojimbo data for use with Dropbox, perform the following steps in order:

1. Quit Yojimbo on all your machines.
2. On your primary Mac, locate your Yojimbo data folder (/Users/USERNAME/Library/Application Support/Yojimbo/) and move it into your Dropbox folder.
3. Create a symlink named “Yojimbo” in the standard location (/Users/USERNAME/Library/Application Support/) which points to the actual location of your “Yojimbo” data folder within your “DropBox” folder.

   Assuming you placed the “Yojimbo” data folder directly within the “Dropbox” folder, you can do this by issuing the following Terminal command (on a single line; you can copy & paste it):

   ln -s ~/Dropbox/Yojimbo ~/Library/Application\ Support/

4. Launch Yojimbo and make sure it still can access your data.
5. Quit Yojimbo again, and wait until Dropbox has synced your entire Yojimbo data folder to your other machine(s)
6. On each of your other machines:
   • Move the “Yojimbo” data folder which is currently within “/Users/USERNAME/Library/Application Support/” aside.
   • Create a symlink between the Yojimbo data folder in your Dropbox folder and the default location as in step 3 above.

At this point, you should be able to open Yojimbo and access your data on any machine, subject to the above caveat that it can only be open on one machine at a time.