Longer Valve Stems?

I am tiling a shower with marble. The substrate is uneven brick. In order to make it all even, I had to float the wall about 2 inches with a morter bed. So now the valve stems from the existing plumbing for the hot/cold are too short. Are longer valve stems (4-1/2 min) available or do I need to re-do the plumbing behind? I appreciate any help as I am very isolated here in Baja Mexico.. thanks!

Most manufacturers have stem extensions available, but you have really added an enormous thickness! 2" mud + marble. Do you have access to the backside, to move the valve forward at all?

Otherwise, contact your manufacturer. It may be available. Also, stem extensions are relatively simple devices. It would not be out of the question to find a local machine shop to make one.