Stopping a Fermentation

I recently found a +5 error in my mash thermometer, meaning that instead of mashing at what I thought was 154F, I was actually mashing at 149F. I would prefer this beer (Brown Ale) doesn't attenuate out that dry. I'm 3 days into fermentation and was wondering if you can force stop a fermentation? I keg, so I wouldn't need active yeast to carbonate.
Has anyone ever tried this? Or is it best to just drink a thinner beer and brew it again next time with an accurately calibrated thermometer?

You could always try cold crashing the fermenter. That should slow if not stop the fermentation. The yeast wouldn't have had a chance to finish there job however (i.e. cleaning up).

I'd let it finish then just add some maltodextrin to boost the body if needed.

Right, that's my dilemma. I don't want to end up with the right body for the beer, but a horrible taste because the yeast can't clean up.
Potassium Sorbate?

The easiest and most reliable way to fix this is to add 4-8 oz of maltodextrin to the beer. Stopping the fermentation is not advisable if you bottle condition your beer, and would likely result in a higher than desirable level of acetaldehyde, diacetyl, and other off-flavors resulting from incomplete or stressed ferments.

Ah, that's a good idea. Thanks!

I personally wouldn't mess with the fermentation. You could run the risk of making the beer come out worty. There's a difference in taste and mouthfeel between the sugars you get mashing at 154 vs 149. Personally I would just wait and taste it when it's done. You could add maltodextrin like someone recommended. What I have done in the past is brewed a beer to blend it with. Why not make another brown ale that you mash at 156 and then blend the two. The you could have twice as much delicious beer too