File Path to Data File

Here is my problem.

I have a solution that i plan to distribute as a runtime application for the Mac platform. The solution consists of two files, an interface file and a data file. The installer will copy the runtime engine and interface file to the 'Applications' folder and the data file will be copied to the users 'Documents' folder.

My problem is that the two files need to be linked together by putting the file paths in FileMaker's 'Edit data Source' dialog for each file. The path to the 'Applications' folder is fixed and simple to achieve as it can be hard coded, however each user will have their own path to their 'Documents' folder and as far as I am aware FileMaker does not support dynamic file paths in the 'Manage External Data Sources' menu. So you can not create a global variable with the path to the users documents folder.

Does anyone have any ideas for a possible solution?

My alternative strategy may be to store the data file in the /Users/Shared/ folder which like the 'Applications' folder is fixed, however this means that each user will not have their own data file.