oh no no, hlspfed is only for debugging.
it's not a proxy as you intend but it's a pseudo proxy used for decrypting the packets that pass through it so you can view them in clear text.
if you want a forward solution over udp you need a classical proxy datapipe like sudppipe:
http://aluigi.org/mytoolz.htm#sudppipebut there is a problem, using a proxy is ever a VERY BAD idea because the ping raises and the performances are not so good because the packet must be handled 2 times.
anyway:
sudppipe SERVER 27015 1234
so if the client connects to the port 1234 of the machine where is running sudppipe, in reality it will play on the SERVER one:
client -> you:1234 -> SERVER:27015