If I understand your requirement correctly, you would like an enhancement to the Shopping Cart Rules that will allow you to apply a certain discount amount, only if the Tier Prices conditions are not met.
If this is the case, I can build an extension that will do this .
I am an experienced developer with more than 12 years in the software world. I have 7 years of experience with Magento and I'm a Magento Certified Developer Plus
During the day, I work as a Technical Architect for a top US based Magento implementation partner, and have worked on some of the biggest Magento Enterprise implementations in the world.
Please let me know if there are any questions I could answer which could help you in choosing the right candidate for this job