ok, thought you don't care about the menus. In this case, DvdReMake Pro can do what you want but it's not a simple-click process as DRMP gives you the freedom to do whatever you want, within DVD specs that is.

I don't know what the structure of your DVD looks like, but if each video is in its own VTS and has the same aspect ratio and audio attributes as the other videos, you can copy all the videos and append to the end of the first video. Then delete the other video VTSs and associated VMG Titles. Then fix the menu to redirect to the appended videos.