I'm waiting for their answer to my question but overall I would say that I am prepared to give them a try.
If I don't find a suitable adapter ring with the shipping I'll either follow AgX's suggestion or maybe try a faster dark-cloth-and-adhesive-band approach.
I only need this to take a few pictures in fact: for each new negative film material I need to take a picture of an IT8.7 calibration target so that I can make a "film profile" for my scanner. That means a single shot or two (daylight - shade) for each type of material, I might go the makeshift route instead of going for maximum exactness.
Thanks for your gentle collabation friends