True, but you would had identified the environmental aspects of such an arrangement (purchase/procurement) and would need a method to control. Isn't control through the purchasing process the easiest? You can use any other methods if they work!
I do agree with you yet I still believe what the standard says:
"...identify the environmental aspects of its activities, products and services within the defined scope of the environmental management system that it can control and those that it can influence...."
Based on the above statement, it is clear that the organization has to identify the env. aspects
within the defined scope of the environmental management system . In this case, the remotely located deptt. is not covered under the scope and hence, IMHO, the persons working offsite may be exempted from being considered as
'working for or on behalf of the organization' so far as applicability of its EMS requirements matter though the organization can not only influence those aspects but can also control them but for certain reasons, it doesn't want to include in it's current scope of EMS.
Do the org. still needs to ensure competencies of those employees with respect to its significant aspects ?