With the new limit algorithm coming soon I don't think adding extra headers for the refresh moment will be very useful. 

One way to make it less smelly is if you store the time when the header is 1/500 then you know when your 5.minutes is starting. You could use that to time your sleeps better when you fear you are going over the limit.

There is also a script on http://docs.shopify.com/api/tutorials/learning-to-respect-the-api-call-limit that uses the processing time of the call to determine the sleep needed to not hit the limit. (Warning, the CYCLE constant still uses 10 minutes as a reset period). You know you can do max 1 call per 0.6 seconds to stay safe, so it's recommended to make sure you do that from the start.

Aside from this, I've been thinking about adding some headers to tell the leak rate and/or time since last call or something similar, which would also be useful for some people. Any suggestions that you would find useful, given the leaky algorithm?