There is no oral agent that can work reliably within a few minutes. Even on an empty stomach, most agents will take about 15 minutes. In my day job I give all these kinds of drugs (and consider myself an expert on them), and I think your editor is wrong -- a benzodiazepine in liquid form would be best.
All these sedative drugs work centrally, that is on the brain, and not directly on the muscles. Specific muscle relaxers are injected, work very quickly, and don't affect level of consciousness. They are dangerous to give to someone in an uncontrolled situation because they paralyze the person (which is, in fact, what we want them to do) and make them unable to breathe.
Among the benzodiazepines you would have two reasonable choices. Diazepam (Valium), the granddaddy of the group, is too slow in onset. Better would be lorazepam (Ativan), which comes as either a liquid or a pill. Midazolam (Versed) also works even faster if you give the IV form out of the vial orally, but it has a very bitter taste that is hard to disguise (chocolate syrup seems to work best at hiding it, but it's still bitter).
ETA: Remember that the individual response to all these drugs is just that--individual. So predicting exactly how a person will respond to a given dose is no more than a rough guess based upon body weight. When I want to produce a specific level of unawareness in a patient I nearly always have to titrate the drug, giving dribs and drabs until I have the person just where I want them to be.
