"its impossible to access I2C memory like any external memory."

That's what I thought initially; but the man from Keil he say, "Yes! - it can be done!"

"Because I2C was much slower than a MOVX instruction. So you need always a subroutine to write or read a single byte."

Of course, you still have to implement the underlying functions to support the XDATA Banking, and timing will still be an issue.
See http://www.8052.com/forum/read.phtml?id=27291&top=