To the best of my understanding this is implicit no matter what you put in your license. Federal law stands whether you mention it or not. If the existence of this condition makes something non-free then there's a lot of software that is non-free; for example rather a lot of Gnu code that was written in the US. http://www.eff.org/CAF/law/software-export-law has lots of stuff that seems related including specific mention of software with encryption capabilities; Squeak may well count (DESPlugin, MD5Plugin etc).
Which was written in Argentia, fortunately. Now if we put the primary download site into the Netherlands we should be pretty safe in this respect ;-) Good thing that SqueakMap is in Sweden, heh, heh ;-)
Cheers, - Andreas