I know we can keep a .jar in the project directory and refer to it's absolute location, but this isn't good for portability and the Additional Libraries location is not appropriate for project-specific code either. It would be good to be able to use a relative location, or to have b4a search the project directory first, to solve this issue.
You can use relative locations. The path is relative to the additional libraries folder. So you can create a project specific subfolder there and use it.
It's not ideal when using version control though. If relative locations are already in use with the additional libraries folder then perhaps scanning the project folder for the .jar would be a solution?
Maybe in the future there will be another "libraries folder" inside the project. Though there are advantages for having all the libraries (and shared modules) in the same place.
I would like to use specific versions of libraries (for various reasons) that would conflict with other apps if they were installed in the Additional Libraries folder. It would be nice is if the compiler would use the same directory structure as the Simple Library Compiler. Basically, if there is a "libs" directory in the "Objects" directory, use those libraries before looking in the Additional Libraries folder.