NUS Packer only packs Content, Code, and Meta directories into installable WUP Packages. If you look in game directories via FTP you'll see that it's relatively the same. Basically all channel forwarders are is just an RPX given an installable title. It's Content and Meta directories are usually empty or just have a simple Dummy file as a placeholder (Meta usually is an exception as it has title information such as the title name, title icon, etc.). The only thing it will have is the App's RPX Executable in the Code directory. So that means if you already have an RPX of said app you'd like to make a forwarder of you can simply get a small VC Game like Link II from NUSspli and cut out the un-needed content, then proceed to replace the RPX with your own; and then you'll have a forwarder.
Now if you don't have an RPX already at hand then this becomes a little more complicated - if you don't feel like porting and re-writing it to WUT and to support using Forwarders you can always do a simple Haxchi installation, and instead of it linking to load Haxchi, you can make the file link forward to an existing ELF on your SD Card. Since basically all this does is make a forwarder out of a DS VC, it doesn't really matter if it's a legitimate title or not (as determined by the ticket) as only CBHC would brick via this way, and setting up normal Haxchi to be a forwarder instead of Haxchi means it won't really touch it's CFW.
