Isn’t the etymology of zhabs tog actually self-evident or self-explanatory? One has to simply come to it! That is, zhabs tog byed would mean something like “to put [someone’s] feet (zhabs) at one’s top or crown (tog)” (i.e. to serve someone or to revere someone). Cf. also zhabs ’bring and zhabs phyi. The latter seems relatively late.
The opposite would be zhabs ’dren (verb “to drag down someone’s feet” or as noun “one who drags someone’s feet down”) and zhabs ’dren zhu ba “to do disservice to someone/something” or “to be a disgrace to someone/something.”