If you really need to encode UTF-8, you can try prepending the unicode byte order mark. I have no idea how widespread the support for this method is, but ZXing at least appears to support it: http://code.google.com/p/zxing/issues/detail?id=103
I've been reading up on QR Mode recently, and I think I've seen the same practice mentioned elsewhere, but I've not the foggiest where.