Optimal struct layout template?

[dsimcha]

According to the spec, data stored in structs is guaranteed to be laid out in
the order specified in the source code.  While this is necessary in some
low-level code, I have a use case where I need to pack structs as efficiently
as possible.  These structs are to be stored in an array, and for efficiency
reasons I want to store them directly rather than storing pointers, so using
classes is out of the question.  Does anyone know how to write a template
that, given a tuple of types, will reorder the tuple so that it will produce
the optimal struct layout?  I don't care, at least for now, if it assumes
x86-32/DMD instead of handling the more general case.