While researching the subject, I've found phrases крыть/покрывать/накрывать (colloquial), делатьсадку, and "подминать" (игрушки). These are probably the closest true translations, even though they don't match "to hump" in popularity or usage.
The following euphemisms and phrases would also work to explain what's happening:
- направляетполовоеповедение (на...)
- возбуждаетсяиплохосебяведет
- выбираетобъектывлечения
So much fuss over a funny four-letter word...
Edit: just noticed @Aksakal also suggested крыть/покрывать
