This version of MIUI (http://forum.xda-developers.com/showthread.php?t=1851262) has an option in the AROMA installer (which will open when you try and install the ROM) which allows you to choose where you wan't your status bar clock (the centre is one of the options).
I've managed to rearrange more then just the clock, i.e. carrier label (with char limit), more icon redesigned and notifications reduced to this single icon, signal cluster, wifi moved to the right of carrier label, battery flipped and bold statusbar text...