Here's the other thing I found out today... ETFs are traded in baskets, and only directly to and from broker-dealers (Goldman-Sachs, Merrill Lynch, etc) to the ETF distributor (IE S&P 500 is Standard & Poor's). For someone to gimmick this, they would need to short all baskets from multiple broker-dealers overnight- because they only buy/sell at market close. The fluctuations we see (read -> we ignore) throughout the day are only a result of the distributor's previous day's selection volatility in individual stocks acting as a collective. The number of 'shares' of S&P 500 doesn't change throughout the day.
That being said, different broker-dealers have different levels of indexes (as in Vanguard using 505 stocks for the S&P 500 as reported earlier in the thread)- and probably multiple 'baskets' with different levels of index within. To keep it fairly even, Fidelity might have 4 baskets with 505 S&P stocks, 4 baskets with 500 S&P stocks and 4 baskets with 495 S&P stocks.
To pull off the gimmic scottish was originally describing, you would have to: (1) align all baskets simultaneously for your company (seems improbable if not impossible because of broker-trader to ETF distributor contract), (2) initiate short sell of the lowest one or two stocks just before close, (3) wait for market close/open numbers to come in and see how well you did based on your vested companies now-indexed stock. The problem is you have no control over what other broker traders are doing with their baskets (assuming you even had full autonomous control over what your company was doing with its own) and the market would respond to your sudden sell of a large portion of stock and drop the short-sell right back out of the index (assuming it even made it there in the first place). The % volume of the lowest stocks are tiny. Probably .2% or so. You don't make any money, you break your contract with the ETF distributor (who has a lot more to lose if indexes are seen as unstable) and you probably broke the law. Not much to gain and a LOT to lose (on a personal level).