Reuse existing mappings

Hello - I have a mapping like so:
```vim
nmap <C-W>u :set winfixwidth!<CR>
```

Or similarly, [tradewinds](https://github.com/andymass/vim-tradewinds) creates `<C-W>gh` (and `gj`/`gk`/`gl`) mappings for moving windows. I'd like to alter vim-submode to recurse into these mappings - is this wise, and if so, what would be the best way to go about it?