I generate those with VIM macros. For example, I might type "day", "may", and "buy" on separate lines, move cursor to "day" and then type something like qa

I generate those with VIM macros. For example, I might type "day", "may", and "buy" on separate lines, move cursor to "day" and then type something like qayy3pklli[^<ESC>A]|<ESC>gJli[^<ESC>la]<ESC>A|<ESC>gJi[^<ESC>la]<ESC>A|<ESC>gJi[^<ESC>la][^<ESC>la][^<ESC>la]<ESC>q And then @a to apply the same expansion to "may" and "buy". (Rather than parsing the keystrokes above, it's probably easier to derive keys with similar effects by using VIM interactively).