How do you name S-Function parameters which default to P1, P2 etc

For many years now I have noticed that when I write a c-code S-function, in the rtw file, my parameters end up just being called P1, P2, P3 etc. So maintaining tlc becomes error prone. I have noticed that Mathworks blocks manage to give parameters meaningful names (E.g. Gain) Is it possible to do the same in my S-Functions? I would guess an SimStruct Function to set the name string? I have search the documentation & internet but not had any success.