I long for this feature, too. I had thoughts of suggesting some modifier to the variable name to force upper (or lower) case.
Right now, I just use the variables as they are, making sure that my template has the variable names aligned (so that they are in the same columns when expanded). Then, I alt-drag the expanded variables, and ctrl-U to uppercase the letters.
(OT)
Symbols starting with underscore (_) followed by an uppercase letter are reserved for implmentation-defined use. I would suggest #ifndef %FILE_BASE%_%FILE_EXT%_INCLUDED
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