[NTG-context] Gentium Basic/Book

How difficult would it be to adapt the typescript for Gentium (at http://wiki.contextgarden.net/TypeScripts) to use the new Gentium Basic for headings & Gentium Book Basic for text weights (both have Roman, Bold Roman, Italic, & Bold Italic) -- but with reverting to Gentium for characters that aren't in the Basic fonts? --Joel