UBS announced Tuesday it will be adding five recently-public Web 3.0 companies, including Groupon Inc. (NASDAQ:GRPN) to its benchmark index of young public Internet companies, officially called the UBS Next Generation Internet Index.

The other four companies being added to the index are online classified ads operator Angie's List Inc. (NASDAQ:ANGI), digital imaging production company Digital Domain Media Group Inc. (NYSE:DDMG), procurement software developer SciQuest (NASDAQ:SQI) and cloud computing solutions consultancy The Active Network Inc. (NYSE: ACTV).

Earlier last month, when Groupon went public, various asset managers noted the market's appetite for shorting a stock many believed was substantially over-priced was being tempered by the fact there just weren't enough shares available to be lent out and sold short.

But the index to which Groupon is being added to after the close of the market Tuesday is tracked by two exchange-traded notes sold publicly on the New York Stock Exchange: and original recipe note that trades under the EIPO ticker symbol and an extra-crispy leveraged note that can be found under EIPL. And, at least up until the middle of last month, only a couple hundred shares were being shorted (out of a total float of 400,000) for each of those notes.

If traders pile on to drive down those indexed securities, it won't be a big surprise either. Since debuting in mid-July, the Index is down 33.38 percent, mimicking the wider collapse of the Web 3.0 bubble. And Groupon isn't even the worst-performing stock that's being added in this round of revisions.

While the company was selling at $19.27 during lunch-hour trading on NASDAQ Tuesday, 73 cents off its IPO price of $20, two of the other four companies being added to the index have lost more since they went public.

Digital Domain Media Group went public on Nov. 18 at $8.50 a share and is trading at $5.74, off 32.4 percent. The Active Network, which went public in May of last year at $15 a share, was trading Tuesday for $13.04, a loss of 13 percent.

The only obstacle traders might find: the ETNs associated to the index are thinly traded. The leveraged note, for example, has a volume of 300 for the day.