Thanks @orthomead and @whart.
When I ordered the Vinyl Stack Spinner, I inquired as to whether or not they had any of the single-disc models left. That model was simply two of the Vinyl Stack "platters" with a handle attached, designed for pre-cleaning a single LP with, say, a sink’s water faucet (or @shaw’s steamer method). The answer was no.
So I embarked on a search for a similar product, and eventually found it on ebay. It is just about identical to the Vinyl Stack single-LP model: a pair of plastic plates (clear to the Vinyl Stack’s frosted white) just large enough to cover the LP label, with a rubber sealing ring on each to prevent water from seeping in, and a handle on one side. $18.99 plus $2.99 shipping from China.
I got the above product to facilitate washing dirty pre-owned LP’s, rather than putting them on the HW-17 prior to ultrasonically cleaning. For new LP’s, unless they exhibit obvious "dirt" (which is unfortunately not THAT uncommon, found even on the new All Things Must Pass boxset) I will skip that step.
I have my HW-17’s tank loaded with distilled water for final rinsing, and after two revolutions of drying the LP is ready for a treatment of Last Record Preservative. I have procured a bottle of Tergitol 15-S-9 surfactant for my ultrasonic bath mixture, needing only some isopropyl alcohol to complete it.
While I’m here, I must thank Bill (@whart) for publishing on his website that incredible dissertation on ultrasonic cleaning of LP’s, which I need to again read! Bill often mentions the Vertigo "swirl label" LP’s, and I can add one more Vertigo title to his list of recommendations: Chapter Three by Manfred Mann. Though remembered for their early "British Invasion" hits ("Do Wah Diddy Diddy", "Pretty "Flamingo"), and later their excellent take on Dylan’s "The Mighty Quinn", by the time of 1969’s Chapter Three they had evolved into a Rock/Jazz Fusion band, and a good one. Interesting music (I say that as a non-fan of Fusion), great sonic quality.