Ok, this is not a bad idea. I can understand not wanting my website on your coin. How about this... what if there was no unique code and the url was very small on the back, OR possibly laser-etched on the coin edge. so you wouldn't even see the url if you were looking directly at the front or back of the coin?
Also, would you want the design of the obverse & reverse on the coin to be the same?
Even if the website was in invisible ink, it would still be there. That gives the coin less of a "currency" feel and more of a website promotion feel. Right now you're the only person (I know of) offering cool cheap bitcoin collectors coins. Take advantage. Even if they're brass now, you are in a position to corner the market, which after some profiting could lead to silver coins, then gold...
I say you should
design a new back and
sell them for double the price of the ones on your website. Then
include one of your website coins for free with every purchase of 2 or more. You'll make more money, your website coins will get to more people, and you could just end up being the exclusive physicial bitcoin supplier once you work out all the kinks in your operation and gather more customers...
I'd definitely buy one made of pure silver without the website listed. Just sell the brass (gold plated) ones to gather the funding needed to get a batch of silver ones made (then discontinue the brass ones and only use that for your website coins, which you will then give away free with the silver ones). I'm excited for you. This is a great opportunity. I'm just an ideas guy, but would love to partner on this with you somehow if you were interested in building a team for this project.
Or just go ahead and toss me a free coin when you get rich.