Haven't you asked about this a few times before? I definitely responded to a question like this at least one, either in the Garry's Mod Megathread or Garry's Mod Gallery
It's something that probably only Garry can do as it requires editing how the Physics Gun itself works, and as far as i've known, the Physics Gun can't have it's core scripts edited by anyone except Garry and maybe some other devs(?)
This is a question that's better off asked on Facepunch or on one of the places you can contact Garry