I want to simplify the On-Access Scanner categories for you. For this explanation, please think about Low, High, And Default as Categories 1(Low), 2(High), and Catch-All(Default). The Process list is what determines what category VSE will apply. In your problem, you will want to put w3wp.exe in Category 1 (Low). Now, ANYTHING that process does, VSE will scan it in accordance to how Category 1 is configured. So, if you turn off every option under "Scan Items", you essentially just whitelisted w3wp.exe. If your security model accepts this approach, then no exclusions are needed. Should you need to enable scanning options under "Scan Items", then you will want to add the exclusions to that categories Exclusions section.
Consolidated list of VirusScan Enterprise exclusion articles