[NTG-context] How to define fallback font for symbols

Hi all, Is it possible to set a fallback font from which glyphs will be taken if the current font doesn't have it? For example, I'd want to use fancy miscellaneous symbols from the Symbola font using their unicode codepoint without any extra font-changing command (and obviously, I don't want to use Symbola for the rest of the text). Alternatively, setting different fonts for different unicode blocks would also do the trick. Vianney