How to setup dub to use x86 and x64 dll's when appropriate?

[Michelle Long via Digitalmars-d-learn]

e.g., using sdl for different versions and have it automatically 
switch.

What would be nice is if one could stick all the files for x86 in 
one dir and x64 in the others and they will be used depending on 
the build(and copied)

Ideally one can do it for debug and release versions too.