[NTG-context] Using virtual fonts defined with lua-code

Hello, The luatex documentation contains in section "7.2.2 Example virtual font" an example how to define a virtual font "cmr10-red". The font is defined by adding the code to the define_font callback. Does some interface exists in contex/mkiv which allows to use such virtual fonts together with the normal font loading code? E.g. could I move the code for the font to some file ("cmr10-red.vflua") so that a request \font\mytest="cmr10-red" will simply find this file and use the code like vf, tfm or otf-files are found and used when needed? -- Ulrike Fischer