Couldn't you just have a player stip with the output connect to the player equip set up to give knife? ........crude i know but i dont think there is another way? ....i dunno, i dont often map for cs s.
With Valve's FGDs, you place one, ensure that the "Use Only" flag is not checked, then turn off SmartEdit and Add new keys. The name of the key is the classname of a weapon (weapon_knife) and the value is the number of that weapon to give (1).
If you get a new FGD, you can get a nice list of all the weapons you can give, then just tick them "Yes" or "No."