no idea if linux has tools to make forwarders, but maybe with wine ?
Modmii should have an option to create a forwarder, but it might be for Wii.
then, you'll have to convert the channel to vWii using one of JustinOnline tool, or edit the wad manually to replace one .app file.
You'll always have the option to compile a dol yourself by editing the path to the dol to load on SD.
then, you'll have to inject/replace that dol into an existing channel.
in all cases, you'll have a channel with wrong or generic banner animation.
If you want, I have a "generic forwarder" for Wii redirecting to a dol path loaded from a config on SD.
you can't have multiple channel at the same time, but you can change the path without reinstalling the wad.
I also have the sources, in case you know c/c++ and want to add button combo to boot different paths.
Remember these are for Wii, not vWii. you need to convert them before installing to vWii.