Apparently editvoicepack for FSX says it. Perhaps you could "borrow" it from there!!!!
It just does not work that way. Apples and oranges. The voice packs for FS atc are a whole different technology.
In theory, new words can be created from existing sound material, using the same principle of cutting and pasting pieces together but it is really dependant on the voice set whether it sounds just barely tolerable or plain horrible.
An example I quickly put together out of four different PFE phrases I earlier recorded myself for my own use
http://www.saunalahti.fi/~kkyle/pics/other/qnh_pfe.mp3
The sheer amount of manual work is a lot so it may not be feasible in a larger scale.