Autumn,
I believe you are correct in that a sweep arrangement must be secured by a specific security. That would be why we add substitution of security language to the agreement.
I'm not sure about using the same security for two sweep arrangements. I think you can, provided the value is there, but then the substitution of security language would be even more important, should you actually have to redeem the security for one customer and not the other.
Keeping the securities separate per customer is the cleanest and easiest path to take.
Have you called the FDIC hotline? I have a contact in Wisconsin I could share with you if you're interested.
kmg
_________________________
Opinions are my own and do not necessarily reflect those of my employer.