Still assuming that there was a second favor to grant, what about if Uriel influenced Nic's decision to use Demonreach as the location? It set the stage for Harry to claim it as a sanctum, become the Warden, and, ultimately, save his life. Not saying that Uriel thought in exactly those terms, but he may have recognized that Demonreach needed a Warden, and wanted Harry exposed to it.
That kind of long-term thinking feels like Uriel's style. I'm not sure how he could have accomplished it—maybe an unFallen Angel whispered in the ear of a Fallen.
Regardless, it's fun to think about a Big Good playing puppetmaster with the bad guys for a change.