I do regret having to ask this, because I once knew the answer myself. However, due to a system reformat, I lost all my altered file hierarchies within the Valve folder and I didn't backup anything outside of my VMFs, thinking that it would be a simple process to set back up.
In any case, after much searching on the forums and on Google, I cannot seem to find the answer. Therefore, I put it before you, my fellow mappers: how does one export Counter-Strike Source textures so that they show up in Hammer when under the Half-Life 2 configuration? All my web searches have directed me to the GCFScape program, but I remember not having used that to accomplish this before. If anyone has the solution, please pardon my forgetfullness and let me know - I'd be most appreciative (a map I'm working on for a university presentation is now a mess of white textures).