I agree with Craig: great question that just isn't asked often enough...
This is a project to define BAs - projects typically have smart objectives...what are the smart objectives for the BA role? What measures will you monitor to see if the role is performing well and for each measure what target value equates to the role being successful?
What is the scope of the role? I.e. what organisation units are in scope to be defined, where do they operate out of, what applications do they use and what supporting infrastructure? What other organisation units and/or applications does the role need to interact with (and for what purpose - what is the information transfer between the BA role and this external entitiy) that cannot be changed by defining this role (they are out of scope)?
What functional capabilities must the role possess in order to affect the measures sufficiently to hit the targets?
Having defined that, what processes do each of these functional capabilities follow?
For each process, what are the non-functional requirements (e.g. who can run it, how fast must it operate, what is the throughput rate, how resilient does it need to be and so on).
What information will be required by the processes in order to be able to run? What is the source and target of each piece of information (reference back to the external entities defined earlier)?
Any relevant (i.e. could affect achieving the objectives) risk, issues, assumptions, dependencies and/or constraints?
You now have sufficient information to write the Terms of Reference for the role specifiying what the role needs to do in order to be cosidered successful. A design of an environment that allows the role the time, space and resources to achieve this can then be designed.
I have a template Terms of Reference for doing this if you want and template workshop structure (who needs to be there, why, structure and content) if that would be of use to you.
Guy