[XeTeX] aligning characters at their centers

[Daniel Greenhoe]

Is there a way to align characters at their centers instead of at
their baselines?

Take for example
   {\scshape Ee}.
This will produce one big uppercase "E" and one little uppercase "E";
and their lower horizontal bars will be aligned. But is there any way
I can make them aligned at their centers (center horizontal bars
aligned) without using \raisebox?

This has application to book publishing when placing rotated text on
the spine of a book.

Many thanks in advance,
Dan