Doing so this way seems to be possible, but please note: I have not done it before, and I did not follow all the way to the end to make sure that it worked.
First Step: Locate and Download the modpack you want to install into MultiMC 5, I will be using the one that b33f3r linked for me (https://www.feed-the-beast.com/projects/ftb-infinity-evolved/files). Then, extract the downloaded zip file.
Second Step: Open MultiMC 5, and Create a new Instance.
Remember to give it a name, so that you know what it is. Don't forget to set the Minecraft version to the version of the modpack. In this case, it's 1.7.10.
Third Step: Install Forge so that the instance can run the modpack.
Be sure to select the release for the version of Minecraft the pack is in. MultiMC should only show you the versions compatible with the Minecraft version of the instance, but double check. I also recommend using the versions with the Star next to them, as those are the latest recommended builds.
Fourth Step: Be sure to run the instance at least once now, so that MultiMC will download the base files of Minecraft and Forge. Then you'll want to copy the files from the "override" folder of the modpack zip file we extracted earlier to the "minecraft" folder of the instance we just made. Remember we want to copy the folders inside of the "override" folder, not the "override" folder itself.
Fifth Step: Download the rest of the mods! This will probably take awhile, but all of the mods appear to be listed on the modpack page under Relations>Dependencies. You'll need to download each mod individually and place them inside of the mods folder in your MultiMC instance. This is the step I didn't do as it would be too time-consuming, which is why most people prefer to use the FTB Launcher.
Keep on Gaming,