votrechien - 5:05 am on Jul 6, 2011 (gmt 0)
What your essentially asking is for the sapphire to enter the country in bond. We do this all the time- we bring shipments into Canada and then ship them into the U.S.. Definitely not worth your trouble though to do it this way and there are severe limitations on what you can do with the product while in bond.
As someone else mentioned, you are eligible to receive a refund of any taxes and duty if you can prove re-export back into the states. Again, depending on how much this amount is, it may or may not be worth it for you time.
Long story short, there's unfortunately no easy box you can tick and have the item avoid taxes legally. You could mark the item as having no commercial value (you can still have an insured value) and plead ignorance if they ever questioned you but I'm sure customs officials see this all the time when it comes to jewelery and I'm sure you'd perk some eyebrows pretty quick.