SSRS 2005 - Hide an element in the page header when a report item doesn't exist on the page

Question

I have an SSRS 2005 report that has two sections. The first few pages have various data elements and should have one item in the page header. The remaining pages of the report consist of a single list control, and those pages should have a different item in the page header. I'm thinking of putting both items in the page header and hiding one or the other based on whether the list object exists on the page, but I can't figure out how to tell whether the list exists. ReportItems("list1") just throws an error if the list isn't there.