Yes, the credit allows for a weighted calculation approach. Many projects in this situation are able to comply. You will need to enter all the roof area that you hope to use to comply. See the calculator in LEEDuser's Documentation Toolkit.
Question
We don't have enough SRI-compliant roofing to earn the credit, but we have a lot of relatively high-SRI roofing (SRI 70). Is there any way to earn the credit?