is it possible to use a different file for the source in the debugger?

Visual studio 2012

I have a project that has a few .asm files (assembly language code), I have the compiler/assembler set to create a list file for the assembly code and would like the debugger to
use the .lst file for the source instead of the .asm files because in the .asm files the macros are not expanded like they are in the .lst files which makes debugging dificult
sometimes.

One way to achieve this I can tink of is to tweak your project settings, so compilation of the C++ files in question outputs assembly language "listing" files that the assembler is able to process as its input, but no .obj output files (or do create .obj files but later ignore them in the build process). Then use the assembler to compile the C++ compiler's output .asm files into .obj files and use these in the linking step.

This would, of course, require considerable fiddling with the project settings I can't explain in detail off-hand either. It will also most probably have side effects you may not like, like the debugger displaying mangled names rather than neatly readable C++ source names.