Copper pipe extender

We have recently had plumbing installed for a new bath, protruding from the side wall over the side of the bath. After applying tiles to the wall we are now unable to put the tap fittings back on as the plumbing is too short. The actual tap itself is fine, but the hot/cold knobs are not. We can put the handles on without a problem, but the decorative cover (which hides the hole in the tile) needs to screw onto the copper pipe, which we cannot do as the pipe is too short.

I have tried a few different "extenders" purchased from Bunnings, but found they extended out too far, so there was a gap between the cover & the wall once it was screwed on tight.

We only need to extend the pipe by about 5-10mm. Does anyone have any suggestions for the best way to achieve this?

The taps handles are the same as in this basin set from Bunnings:




Stylus Venecia Basin Set - Bunnings Warehouse

We are unable to attach the bell-shaped decorative cover.

Any advice would be appreciated.