Nothing legal is good for this. OTC sleep aids are worthless for helping a bad trip - they're only useful for helping to get to sleep once the majority of the effects are gone.
Etizolam is an option - it's a benzo (well, not exactly - but it might as well be) that hasn't been approved in the US, and as a result is not scheduled in the US. The key with using benzos to treat a bad trip is to get the dose right. They won't counteract the effects of the psychedelic entirely (though they'll dull it somewhat), but they will help deal with the anxiety that is characteristic of bad trips. If you take too much, they'll be fucked up on the benzos - and still tripping - not an ideal situation. So keep the dose low if you give someone benzos for a bad trip. Soma (a non-benzo sedative used as a muscle relaxant) also works for bad trips in the same way that benzos do, and seems to dull the trip more than benzos do.
I'd just try to scare up some soma, diazepam, or clonazepam on the black market (other benzos will work as well, but I've found xanax and lorazepam, the other two common ones, to be less effective at dulling the trip.). Clonazepam is generally the least recreational and most perscribed benzo, so its one of the easier ones to get. I'd give him 10mg diazepam OR .5mg clonazepam/xanax OR 1mg etizolam with the option of a second dose of the same size (I wouldn't go beyond that - obviously the doses should be higher if he's got a benzo tolerance - the objective is not to get high off the benzo, but rather to just have it reduce the anxiety from which a bad trip arises), or, if using soma 350mg soma with option of second or third dose.