Ken Burns effect might work for you
Ive used the Ken Burns effects in FCPX to take an image that is wider than my 1080 screen resolution to do this.
Its pretty simple to do.. After youve created the video you want for the background, import the wider image you want to scroll across and lay it over it. Highlight it and click on the Ken Burns effect. It will give you a start and an end overlay. For an extended (long) image, you may have to do several of these and combine them.
If youre doing this on an older (i.e., slower) Mac and/or one with limited memory, the final compression may take quite a bit of time.
Good luck.