Lot's of plans out there if one is capable of planning ahead (I'm not) and LV will sell you a fixture for $65, but...
...if you're like me, with simple needs and the scrap box always yields something an inch too short or long to make the Wonder Pup work, this is the
< $10 (not counting the pilfered pipe clamp) answer.
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The 5" Nipple unscrews in seconds when the bruise on your hip get's too tender after banging into it several times and the 2 inches of travel almost always allows proper "dogging".