kindle2-feedback [at] amazon.com <-- Not exactly customer support but feedback channel for the product.
I didn't know Vietnamese is not glyph based. Do you have a handy reference to which code plane Vietnamese sit in Unicode?
[VN.net hosts a a group of “designed-for-Vietnamese” Unicode fonts. These fonts have proper diacritic positioning and the increased linespacing required for readable Vietnamese typography. Fonts which are currently available on the site include the Tri-Chlor set, and the Web Fonts set. These font sets feature the 134 Vietnamese glyphs (ký tự Việt trong Unicode) and additional 38 Pali-Sanskrit Glyphs (ký tự Phạn Pali-Sanskrit trong Unicode) required by the Unicode Standard. Float marks, the euro and Vietnamese đồng currency symbols, and the Buddhist wheels, U+ee80 and U+ee81, are also included.] <- reference :
http://www.unifont.org/fontguide/
Update: If you would like to generate a text file and attach it to the forum, I can try to see if I can read it on my Kindle 2.