C functions

Does anyone know if it is possible to define a Postgres C function as taking a
variable number of parameters? The fmgr code will pass it, but I don't see any
way to use "create function" to register it.

Does one have to issue a create function for each additional parameter?

I am trying to port some mysql stuff to postgres, and mysql has a function
"concat" which will concatenate a number of fields. I have this coded for
Postgres, but I can't get it registered. I used a few "create function"
statements to cover the number of parameters I need, but this is really ugly.

(Also, this will help with "decode()," an oraclesque function I use.)