Idea - Casascius Physical Bitcoins and split-key vanity address?

I could do it on my larger denominations, laser etching the vanity firstbits for a fee. This would provide two advantages: first, the obvious ability to vanity, second, I wouldn't know the resulting private key, you would effectively own a two-factor coin, so those of you who worry I might run with your money, this is a viable solution.

Another huge advantage is that this becomes a de-facto long-term bitcoin storage product for newbies with the absolute possible lowest risk of loss available today.

If I do it, here is how it would work:

1. I reveal the public key to one of my pre-printed circles, which you can use for VanityGen. (I kept the pubkeys on my 2nd series anticipating this becoming possible, and the public availability of vanitygen tools that accept public keys as input constitutes the breakthrough that makes this possible!)
2. You VanityGen the resulting address of your choice (or submit it to a vanity pool so you don't have to, or just quickly vanitygen any random address on your CPU if you're not interested in a specific prefix).
3. You submit the resulting public key to me (and keep the private key to yourself). I will also ask you to sign a message with the private key to prove you actually have the private key, but you can choose the message. Alternatively you can use the bitcoin address of the single private key (not the combined vanity result) to send bitcoins in any amount. This just cuts out the possibility of a lot of potential mistakes.
4. I create your physical bitcoin piece. The hologram will list the vanity bitcoin address address which I will professionally laser-engrave. If the item is a bar, I will also chemically etch (in black print on the bottom of the bar) the URL "casascius.com/twofactor" (no content at the URL yet) and part of the bitcoin address of your public key (only part will be shown specifically so no one thinks they should send BTC to it to fund the bar). The text at /twofactor will explain that the piece is a two-factor piece and can only be redeemed with the private key whose bitcoin address matches X, so that the bar remains transferable to another party: one can independently verify that they received the secondary private key without actually having to open the bar.

I estimate charging an extra $15 for this process, given it is 100% manual and work that requires care, which clearly only makes sense for the larger value items. I probably could do it to the 25BTC and 10BTC coins as well, it just doesn't make sense to etch the metal piece.