If you haven't already done so, you should definitely review the Interpretation Guide for section 3.5.1.7.
The intent of the "exception" process isn't to allow you to totally abdicate all responsibility for supplier and raw material controls - for example, it makes the very valid point that you need to ensure that you can assess and control the risks these might pose to other products.
Whilst the IG doesn't define the nature of an "exception", I think it is a reasonable inference to conclude that this is intended for occasional use, and therefore shouldn't/couldn't be applied to *all* raw materials.
Have you tried discussing with your customers? Having previously done contract packing where the situation was the same as yours, i.e. none of our own raw materials, I didn't have many issues getting BRC or equivalent certs, product spec, allergen info etc for each raw material. Particularly when I told customers that I couldn't reasonably accept their materials onto site without this, and so would be forced to turn their deliveries away, and potentially charge them for the missed production slot that would result from this
Obviously I'd suggest starting on a somewhat less pushy footing - explain why you need this, for example allergens are an easy one as no customer is going to want to recall their product because a different customer forgot to tell you they had nuts in a raw material, so they should be able to relate to this and understand why it's a reasonable request.