Well, you could certainly create a potion of Sleep targeted at the imbiber. If one intended to use such methods often, a Daily item would be a better choice.
For herbs, RMU would offer Arunya and Hugar. Wek-baas can cause sleep, but has more dangerous possibilities. Hith-i-Girith would require risky harvesting and be more difficult to employ, as it is inhaled rather than ingested. But then, the listed herbs are but suggestions, and the GM should not feel either obligated to include a listed herb nor limited by what is listed.
Simply drinking your companion under the table is a slower alternative, perhaps more interesting to play out.