Combine Blu Rays

I have Lord of the Rings Extended Editions on Blu-Ray. I've ripped them onto my computer, and they're in their original format, I haven't done ANYTHING to them. Is there anyway to create a new "Blu-Ray disc" (In name only, it'll be JUST files on my computer, not actually burned to a disc) where I can combine each part of the movies into 1 part (So I end up with just 3 movies/files), then turn them into a Blu Ray with a custom menu? I want to preserve the DTS-HD Master Audio 6.1 audio and the MPEG-4 AVC 1080p resolution. I realize this is going to be almost 200GBs, so like I said, I won't actually put it onto a disc, just keep it on my computer for software playback.