Something like this should work. Credit to Peace-Maker (if I remember correctly).
PHP Code:
#include <sourcemod>
#include <sdkhooks>
public OnClientPutInServer(client)
{
SDKHook(client, SDKHook_PreThinkPost, Hook_PreThinkPost);
}
public Hook_PreThinkPost(client)
{
SetEntPropString(client, Prop_Send, "m_szLastPlaceName", "");
}