How to Log In to Flickr in iOS 7 with a Google Account
The work-around solution I've found for this does not require "starting fresh", though it does involve some degree of "new" account creation. You must create a new user@yahoo.com email address linked to your existing account using the method below:


Visit yahoo.com
Click the "Sign In" option at the top right
Choose the "Google" option to sign in with a Google account
In the pop-up window that follows, log in with your Google/Gmail account
Click on "Mail" in the top right
Follow the prompts to create a new yahoo account, using a new/available user@yahoo.com email address
Once this process is complete (was a bit "buggy" for me when creating, asking for password re-prompts then giving errors, but still did actually work), you should be able to use the username (e.g. the "MyUserName" from MyUserName@yahoo.com) and password you chose to log in to Flickr; I recommend visiting flickr.com and using these yahoo credentials to ensure your content is present as expected
If all of the above was successful, you should be able to connect iOS 7 to Flickr via Settings > Flickr by logging in with your yahoo ID and password