A year or two ago when I looked into this, there were German companies selling adapters, etc. to put smaller halogen lamp bulbs into larger sized sockets as there was a class of lamps that were exempt for various reasons, e.g. reading lamps, oven lights, etc. Especially special applications like terrariums, etc.
I haven't checked, but you may wish to find out if the adapters are still allowed. If they are, then great!