No magician shall ever give away the secrets of his trade ;o)
Pretty much like you said: I stuck a short twig under the chainstay. It had to be slanted a bit and it was all but stable, but it did the trick for the two or three minutes of the photo-shoot. From there on it was just a bit of cloning and healing in the GIMP.
For a 27.5 I’d hesitate between the Jeffsy and a Canyon Spectral; the latter is not available in 29, though.