The Philips Hue wireless dimmer replaces the wired light switches used by ordinary bulbs when you replace these with Philips Hue lights. For some unknown and completely mysterious reason Philips decided to make the base place of the dimmer slightly narrower than the standard width of European light switches. The "normal" width of these is 84x84 mm with a hole width of 60 mm. If you just remove the existing light switch and fasten the dimmer using double sided tape, the result will be very visible marks from the old 84 mm switch. This is naturally completely unacceptable.
Another problem is that the dimmer is higher than 84mm, so the normal cover plates for electrical mounts are useless as a base for mounting the dimmer.

This design is for a plate that can be fastened to a standard light switch mount with standard screws and then serves as a perfect base for attaching the Hue dimmer plate. The result looks pretty nice.
Using the bottom of the print as outer surface produces the best results. You have to manually countersink the holes for the mounting screws with a small file or a drill.

The plate is available in two versions: One with just two holes in the middle. This works if the electricians mounted the switch holder in the standard way. The other version has a plethora of holes that make it possible to mount the switch rotated or in any of three different heights, while still completely covering up the old mount.

The original FreeCAD drawing as well as the printable STL files are available for download.

You want to print with a high infill level, say 75%. Otherwise the plates will bend in the middle when you tighten them down with the mounting screws. You can print with coarse settings (0.3mm) and high speed since only the base of the print is visible. I pushed it a bit to far on the multi hole plate in the picture, which I printed at the absolute maximum speed for my printer. This produced uneven holes and crap on the border.