I remember a few small theatres had 'hip systems' that used dimmable fluorescent 40W tubes setups - according to the the guy who knew about working them, they were a pain, and did not all extinguish together, especially as they aged.

"EU regulations won't allow frosted glass bulbs unless they're A-rated, so these are all in clear glass, which throws horrible shadows"

You can try etching the external surface - that's what they do internally, but who wants to muck about with highly toxic fluorine... there are coatings which may help, but if your fitting will take it - you can buy theatrical/photographic lighting plastic 'color film' called generically 'gels' - which come in a large sheet - various colors (including photographic 'color temperature correcting' shades) as well as frosting of several grades. Or you used to be able to get it easily, but the world is changing...

One old coating trick was to use a hot saturated solution of Epsom salts - magnesium sulphate - to coat windows - but it may not like the heat of a hot bulb. When it cooled and dried, it would form a thin sheet of white crystals.