This is a pretty old question. Just post a solution that might be helpful to others.
I use ProxyPassMatch, which is equivalent to ProxyPass, but allows the use of regular expressions.
Consult Apache HTTP Documentation
Example:
ProxyPassMatch (? I) / abc http://mydomain.com/handle-all-variants-of-abc
This will match all combinations: (abc, abC, aBc, Abc, ABc, aBC, AbC, ABC)
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