I think you should make a motion menu.
Maybe something like this :
Make your Menu (and the button layers) in Photoshop with your still photo background that you want to show it in Encore. Save it with the name (for example) Menu.PSD
Make a motion menu within your video editing app.
Within your video editing app, import as composition your Menu.PSD file
Make the composition in the timeline something like this :
1. your still frame for (say) 12 seconds
2. 2 sec of your button layers starts on the 10th second with 1 sec transition then end at the 12th sec of the timeline.
Export the timeline to a compliant video (DVD/BD) format.
Name this video (for example) FirstPlay.m2v (m2v is the extension for DVD compliant file).
If you play this video, you will see
- 10 seconds of your still frame without button
- 1 second of your still frame with button transition
- 1 second of your still frame with button (exactly look the same with your Menu.PSD file).
Within Encore :
Import the FirstPlay.m2v to Encore as Timeline
Import also your Menu.PSD as Menu, name it (for example) MainMenu
In the Project panel, right klik your FirstPlay timeline-icon and choose "set as First Play".
In the FirstPlay Timeline Properties panel, set the End Action link to your MainMenu
Click the "Preview" icon.