i do something similar using the appskey or printscreen key as a modifier so i so i only have to use my right hand. i used lp;' instead of the usual hjkl vim keys though.

  printscreen::
  thumbMod := true
  return
  
  printscreen up::
  thumbMod := false
  return
  
  
  #if thumbMod
  
  l::    send {left}      ; move caret
  `;::   send {down}
  p::    send {up}
  '::    send {right}
  
  +l::   send +{left}     ; select text
  +`;::  send +{down}
  +p::   send +{up}
  +'::   send +{right}
  
  ,:: send {backspace} 
  .:: send {delete}
  
  #if