Training the Western Pleasure horse for Barrel Racing?

My western pleasure, English pleasure, hunt seat, and jumping horse has been trained to go slow in a western saddle but to go at the slightly faster pace for English. I am trying to train him for barrel racing(then we will add down and back, key hole, poles, and the rest) I have him trotting through the barrels quite nicely but how can I get him to do a fast canter/lope and to eventually gallop without speeding him up out of Western pleasure to much?