NO NO NO NO NO NO NO! Brake fluid does all sorts of VERY BAD things when you use it outside of the brake system! It eats paint, it rots rubber lines that are not specifically designed to be in contact with brake fluid, and Dot3 fluid is EXTREMELY FLAMMABLE!

A MUCH safer method is to use a non-flammable carb/choke cleaner. Rather than the engine gaining RPM and potentially damage it due to detonation, the engine will choke out (or at least lose some RPM) if you spray it at a vacuum leak source.