Get someone to add a Brazed on fitting .. on that strut you got lots of frame builders in Portland. hire one to do the job

if its chromed .. they should be able to Fabricate something to firmly Bolt around the strut.

OR buy this and enlarge the hole for the quill bolt to pass thru Stem Cap Light Mount from Paul Component Engineering

How about the other side of the handlebar ?

or the Tube Ones that go on in place of the nut on the QR skewer ,

You can fit a Planet Bike wired Dynamo Super Flash on either its a handle bar mount. , & take it off and pocket it, when you park



this will go on the non Bell side of the bars ,. too Mounting Lights from Peter White Cycles for the bolt on headlights.