There do exist add-on nipples for just this purpose... but, sadly, I'm having a hell of a time finding the vendor I found previously. They're easy enough, a nipple with a flange at one end and threads and washer to lock it down; The other end has a bead or conventional hose barb.
Someone's posted info on them on here before IIRC... maybe you'll have better luck with a search than I have.