The technique has been mentioned periodically in different posts here in the forum so I can't specifically point you to those references.  Essentially, if your clothing morphs match the model's, simply selecting the model, go Edit>Copy, select your conforming clothes, go Edit>Paste should translate the morphs.  But there is a given condition, the clothing morphs must match the model or the process will not work.  The program Morphing Clothes by Dimension3D will add character morphs to just about any conforming clothing item and is an excellent way to get that exact fit without the pokethroughs.  I have used it and it complies with the copy & paste I just described. 
Magnets aid in creating morphs. IIRC, once the morph is created, a spawn is generated which actually places an extra dial in your clothing properties.  Afterwards you can change your new clothing to your library. 
If you get the opportunity, check out Morphing Clothes.  It maybe the solution you're looking for.

http://market.renderosity.com/mod/bcs/index.php?ViewProduct=64629&vendor=288865