If manufacturer/brand is the only criteria/rule - I can only think of using each of the other manufacturers in the rule - that is 'Manufacturer in the Cart' - 'contains' - 'XYZ' brand for the brands that are eligible for the $5 off. Assuming Brand is setup as the Manufacturer. If it's a strict rule - then I would think each manufacturer/brand would have to have a separate rule.
If you carry a number of brands - this may be very time consuming and impractical.
It may be something to then drop into a feature request to have the 'not contains' programmed in. I'd vote for it. We would find it very useful too.
Thats all I can see in there. If there is another way, I'd like to know as well.
Manjula