Hi Chunk
When I bought (won) a bargain "beer-engine" from a seller on eBay (who said they had retrieved it as part of a pub clearance, and judging by the description, didn't have a clue what they had), what actually arrived was a
Mason Shakespeare Dispense Unit (link). The page on the Mason's website has changed recently, and it now only describes the purpose of this for in "pumped systems", but it used to also mention pressurised (keg) systems.
Basically, this is a tap connected to a hand-pull, that opens the tap when the lever is pulled, and lets pumped/pressurised beer flow through the swan neck (with or without sparkler/creamer) fitted ... admittedly, I don't have cornies, I connect my handpull up to a (basic) pressure barrel (like Jim describes over on
that thread (link)) and found that, because I had one of these cylinderless units rather than a "proper" beer engine, I didn't need a check valve ... however, the beer does end up a lot more "cask like" after being served through this setup ... and I'm sure connecting up a corny would be similar to a PB, in principle
I don't know if this helps you solve your "problem" ... but it does demonstrate that there is someone out there that has done this before, so the "problem" can be solved
Cheers, PhilB