Hello Lorne - There is another option you can try that has been successful for me. If the sale wasn't too long ago and you think the buyer will remember you (and may be otherwise happy with the transaction), try sending him a sweet-as-honey, very polite email asking if he'd consider revising his feedback and explaining the circumstances.
You can mention for example how hard you try to make shipping reasonable for your buyers, that you sympathize with his frustration about shipping (whether you do or not ;-)) but explain how important your feedback profile and your reputation is to you. Let him know that if he agrees, you'll send a request through eBay. There is a page for this: "Request Feedback Revision" that if I recall correctly can be accessed through the feedback screen on your Summary page, and possibly also on the drop-down menu for the item on your Sold list.
Many buyers have no conception how critical a couple of negative or neutral feedback entries can be to a seller, and sometimes such a plea can work. If he doesn't reply, you've lost nothing but a few minutes of your time; if he does, then you can send the formal request through eBay. Important to note though: I wouldn't just send the formal request before contacting the buyer, as the screen on that page just doesn't give you enough room for explanations, etc.
Your final option, if the above doesn't work for you, is to enter a Reply to the feedback that will be permanently shown under his comment. You're forced to keep it really short, but at least it may show other buyers your side of the issue.
Believe me, shipping is THE #1 problem I deal with all the time! I constantly discount shipping charges for my buyers, yet I still sometimes get less than perfect DSRs on shipping costs.
Sorry about the long reply, hope this may help!
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