Welcome to
A flat driver from a Wave or Rebar or perhaps the Micro Bit driver should work in there, space is kind of limited for height, so it does limit the options
I have never modded a Signal though and most do keep the awl, so I haven't personally seen anyone replace it
either way, good luck and I hope you can find something to your liking
also, let us know what you do end up deciding and pics are always awesome