The standard client is open source software. Just add a setting to display amounts in Bitcoins, Millies, Mikes or Satoshis.
If you're not a programmer, start up a bounty for a programmer to do this.
There's no possibility to change the definition of what "one Bitcoin" means. You can't have one name meaning different measurements. But using sub-units instead of the largest unit is unproblematic. Go for it!
I am a programmer and I could change it. However this is not a coding issue in the slightest. It is a community issue. We need a consensus. We all need to switch at once. MtGox and TradeHill need to switch. Bitcoin.org will need to switch. The vendors would need to switch. In order for that to happen we all need to agree. That is what I am trying to do. I am trying to convince you.
It is entirely possible to change the definition of "one Bitcoin". Mexico did it with the peso. The chopped three decimal points off in a country of millions of people, many of whom live in remote areas and/or are poorly educated. The bitcoin community is small and well-connected. If we all agree to do it there would be no problem.
Perhaps the best that I can hope for is to get everything listed in bitcents and drop the notion of bitcoins.
It's as simple as changing the front-end GUI. This could of course confuse people if they use different versions of the client and see different amounts of BTCS. But if it bothers you that much make the change and distribute it either in the GUI or by changing the protocol (if your mad).