1) Get a title id of any game you have installed from http://switchbrew.org/index.php?title=Title_list/Games (this is your target titleid)
2) Create a directory on SD : sd:/atmosphere/titles/target_titleid
3) use hactool to extract the romfs.bin and exefs files from your main game nca (its in secure from XCI - the biggest one)
4) put romfs.bin in sd:/atmosphere/titles/target_titleid/romfs.bin, exefs files into sd:/atmosphere/titles/target_titleid/exefs/
5) Edit titleid in main.npdm (in exefs) to contain target title id (this might help http://switchbrew.org/index.php?title=NPDM)
6) run a fs_mitm containing CFW release, run your target app
Note that saves don't work for me atm, Simon claimed he made it work, so you might wanna wait for his way.Minecraft works, others not tested.