Sorry, but I’m not sure I understand the question.
It sounds like you have a button on your menu which you set to be an animated button- it shows a preview of the clip it links to. But you don’t want it to be a button, you just want it to be a background. Is that right?
If so, two ways to do it-
First, the simple way. Customize the button routing so that the user can’t actually click on the button. The downside- if the user is playing the DVD in a PC, they’ll still be able to use the mouse to click on the button.
Second, the right way. Take your whole menu into After Effects or Premiere, and add the video that you want in there and export it as an MPEG file. Import that into Encore and set it as the background of your menu.