dummy up

verb3

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) 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.