Too many things are going awry here:
A.) If we are talking soil here, and the beer is supposed to be 'flat', then I'd say make sure its really flat then aerate it with an airstone.
Not only does the plant not need much CO2 at the root level, it actually needs O2 to uptake nutrients, and thwart the growth of pathogenic anaerobic microbes.
B.) Any benefits you are trying to see from adding yeast as a microbe with cheap beer are mitigated by the brewing process. Oftentimes, the yeast is what gives beer its "signature" flavors. Many macrobrewers (large breweries) ensure that all yeast are dead or filtered out as a way to ensure clarity in the beverage and so potential competitors do not extract that specific yeast strain and copy their beer recipe.
C.) The sugars in beer also may contribute to a significantly higher population of harmful bacteria in the rhizosphere, raising pH, and possibly causing pH related nutrient lockout.
Word of caution: Don't go balls deep on your whole crop without trying this method on a small scale first (ESPECIALLY INDOORS). At least it can be washed away outdoors.
Lastly: This is the author's qualifications when writing this article,
Taken from
http://www.hackcollege.com/blog/2011/08/31/beer-the-multipurpose-alcoholic-beverage.html
"ABOUT THE AUTHOR
Laura Schluckebier (whose last name is German for "drinker of beer") is a student at Trinity University in San Antonio, Texas. She's a double major in Communication and Classical Studies. She watches way too much TV and is a diehard Joss Whedon fan. She's the Associate Producer of the Trinity student-run show and hopes to one day pursue a career in television. Her favorite things in life include Torchy's Tacos in Austin,
Battlestar Galactica , and her well-loved
Harry Potter books."