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I was thinking about this a little more and did some quick checking on some things.
It sounds like you are outsourcing your editing or doing something like that.
The latest DNG spec actually makes references to "Proxy DNGs" with the implication that someone could edit the lossy-compressed (and possibly resolution-reduced) versions of the file and then those edits could be applied later to the full raws.
Creating the proxies is pretty straight-forward using the Lightroom Export dialog, with the lossy compression reducing the raw file size by about a third and with resolution reduction reducing file size even more.
What I have not been able to find, however, is the process for getting the edit parameters associated back to the original raw. You might want to ask this question on the Adobe Lightroom forum and see if someone there could help you.
If I was going to do some experimenting on my own, I would create side-car XMP files from the edited proxies and see if I could get those to associate with the original raw files. If something like that works, it could mean that the trip back from your editors could be even smaller since they could just send the parametric adjustments without the actual image.
There are probably limitations to this process, particularly when extreme highlight and shadow recovery is involved or when making fine healing edits but it would probably work pretty well for general edits and white balance.
Good luck. Please let us know if you find a workable solution.