It’s a common thing to happen There are rubber bungs that are supposed to hold it on the rear of the fan housing but people fit a jubilee clip on the rear as a simple fix
Or, as you suggest, make a simple metal plate that screws to the fanshroud that holds the tube in. I had to, as they have a great desire to go walkies.
I tend to cut a short piece of fuel pipe along its length, clip it round the tube behind the fan housing and (as @paradox says) secure it with a jubilee clip. Might have added a washer against the fan housing too. It’s piece of mind as it’s pretty tricky (but possible) once the engine is in place.
So far for me the throttle cable bowden tube outer has stayed put, its meant to be stopped by part of the gearbox support, as the outer has a stepped ferrule that rests in the hole in the frame, so the tension is taken by solid metal not friction on the through fanhousing tube. The stock grommet on the tube through the tinware is also pretty feeble. I managed to push that one off refitting the engine. Something strange there...maybe aftermarket bowden tubes arent right.. On my bus, it has only been the tube through the fan housing rattling about. A cable tie round that tube behind holds that in place, as there is no tension on the tube.
