Valid ePub already has to be UTF8 or UTF16, no other code page is allowed. Granted I agree that I have seen badly encoded ePubs as well, but usually the ePub won't display the characters correctly in that case.
You might want to check this page:
http://freekindlebooks.org/Unicode/unicode.html
If the Kindle can support that character or a similar glyph it would show up in one of those test files. You can use search and replace to search for the any variant it does support.
I suspect 'transliterate unicode to ascii' might be your only option that doesn't require hacking the Kindle's fonts, etc.