The fabled Schrader to Presta adopter aka "damsel in distress" valve that we used to make from shop parts to carry on rides.  Specifically to be able to help out young ladies with flat tires and our presta only pumps.  Knowledge lost from my TBI.

I made a protype of a hardware store grade schrader chuck with lever, presta valve from an old tube and plastic hose between but it was only a prototype.  Took it to Portland's ace shop.  A middle aged mechanic took interest, had several good ideas, suggested Portland's ancient hardware store and Citybikes, my next stop anyway.  At Citybikes, more ideas and a report back that he found one on Amazon under schrader to presta adopter.  Yes, one was there among 2 pages of presta to schrader for $8. 

You know I hate dealing with Amazon and cherish my account free status.  So I kept looking.  First non-Amazon hit was Cantitoe Road, an e-bike dealer.  $9.60.  Nice write-up describing exactly what I want it for.  Sold!  Bought 6.

Question to be determined - how much air do you lose unscrewing the valve?  I'm guessing there is a time window when the adopter has broken the air seal as you start to un-thread but the button on the tube valve is still depressed.  Will I have to invest in a schrader wheel to acquire the skill?    "Hi!  I'm looking for a bike wheel with tire and tube.  Has to be schrader."  Size?  "Doesn't matter."  Type?  "Doesn't matter."

For many years there was a resource I could have tapped into but those adopters were only passing thoughts and I never put the pieces together.  Sheldon Brown.  He knew.  He was close with our shop mechanic.  Stopped by the shop to hang quite often.  Those damsel in distress valves came up in conversation frequently.

If this works, I'll be going to bike shops and showing it off.  Simply a better world where elitist cyclists can carry a tool to help others (and do it with pride).  Yeah, yeah, we all can flip that little gasket around in our pump heads, but small black parts love to run away.  Giving them slopes to roll down and vegetation to hide under (the typical roadside) is tempting fate with a big carrot.