[NTG-context] Automatic character replacements/substitutions

Hi, Can someone please help me remind how to automatically "replace" a Greek letter (gamma (γ) in particular, but I wouldn't mind if the whole alphabet would be replaced) with $\mathgreekupright γ$. The OpenType font (Lucida) doesn't have Greek characters (except for maybe μ), but the math alphabets in the math font are complete, so I would like to automatically use the characters from the Greek math in main text (possibly upright math in upright text and italic math in italic text). Of course I can always create a shortcut for $\mathgreekupright γ$ but it would be great if things like "γ rays" or "α particles" would be typeset "automatically". Thank you very much, Mojca