[Closed] Shower/plumbing advice required

I've got an Aqualisa concealed shower with a fixed head/arm.
The head was knackered to I decided to change it. On closer inspection, the head/arm interface features non-standard threads, so I also decided to change the arm.

However, the original arm used some sort of push fit system; upon removing the arm all that's left is a bare copper pipe protruding from the wall at a right angles.

This is a problem because all the replacement arms I have seen (including the one I have) need to screw into something.

What do I do?
I really don't want to have to rip tiles off and dig around in the wall if I can avoid it.

I've seen some push fit/fast fit arms that look like they might be suitable, but at £50 I thought I'd see if there was another solution.

Thanks!