[Q] MultiRom kernel flashing?

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http://forum.xda-developers.com – I got Paranoid 3 as my internal rom, running franco kernel. However, gaming and file transfer with computer seem slow and laggy as a 2gigs movie took 15 mins to copy from pc to nexus 7, so I'd like to install stock rom and stock kernel as an alternative I can use when I want to transfer files. The problem is Multiboot only allow separate kernel for external roms as boot.img, and the kexec patched stock kernel (any many other kernels) is only released under .zip flashable. So does anyone have any solution to this? Please tell me :) (HowTos)