dummy up

dummy up (third-person singular simple present dummies up, present participle dummying up, simple past and past participle dummied up)

1. To make a mock-up or prototype version of something, without some or all off its intended functionality.

   The carpenters dummied up a set of simple props for the rehearsals.

2. To make a fake version of something; to make a counterfeit.
3. (informal, sometimes imperative) To suddenly stop talking; shut up; to keep a secret; to refuse to talk.

   When he couldn't think of any more good lies, he just dummied up.

   Everyone was discussing the new teacher, but when she entered the room they all dummied up.