Use a launch stooge. Look here, http://www.clcombat.info/stooge.html That will show you some different types mainly for combat models.

Also look here, http://rulecombat.com/ same deal, it's for combat models.

My favorite type is pictured below. I have used this with a Hyper Viper the only change I made was to bend the Viper's tail skid into a loop at the end to engage the launcher.