Back in 2004, Carter and Jeukendrup (Med Sci Sports Exercice 2004, 36: 2107-11) had already verified an improvement of 2.9% compared to controls in a time trial effort of cyclists performing a 5 seconds mouth rinse with a solution of CHO every 8 minutes, without swallowing such solution. 

Furthermore, Chambers and Al (J Physiol 2009, 587:1779-94) confirmed an improvement of 2-3% with mouth rinses of glucose and maltodextrin solutions at 6%, lasting 10 seconds every 8 minutes of effort; with the help of magnetic resonance (MRI), they noticed the activation of brain areas related to motivation and gratification during exercise. 
The artificial sweetener placebo did not improve the performance nor activate brain areas. 

Pottier et al (Scand J Med Sci Sports 2010, 20:105-111) verified on 12 triathletes an improvement of 3.7% during a 1 hour time trial effort compared to placebo, confirming that the rinse decreased the perception of fatigue allowing to develop a higher power output. 
Surprisingly, the ingestion (without rinsing) of the CHO solution did not produce any improvement in performance, suggesting that the DURATION of the contact of CHO with the oral cavity was the factor determining brain stimulation. 

Personally, I could verify an improvement of my own performances over time trial efforts of 20-30 minutes, simply by holding CHO solutions or gels of maltodextrin in the mouth for 12-15 seconds every 10-12 minutes, compared to the rapid ingestion of the same. 
Probably the digestion and absorption of CHO (which are not required for events of this duration) removes blood and energy from the muscles involved in the effort. 

For longer events, my advice is to hold CHO solutions and gels of maltodextrin in the mouth for 12-15 seconds before swallowing and not to drink water in the following 5 minutes.