Just a quick one to collect any good ideas.

Got a bath tiled all round to half height. But now I want to stick a
shower head on the wall so want/ (need?) to tile right up to the
ceiling within the shower area of it.

Now, the lower tiling was done over the older tiles so sits quite proud
of the wall so any new tiling above needs to be at the same level.

So, my question is, what's the best way to pack the wall out to the
same level before tiling?