Looking around on google I found this software, not sure if it is what you are looking for.
http://www.softpedia.com/get/Multimedia/Audio/Other-AUDIO-Tools/Multisine.shtml
You could run it under wine.
Oh... before the additional note in the original post, sorry.
Edit: Woohoo, found one!
http://www.comp.leeds.ac.uk/jj/linux/siggen.html
Apparently the software Audacity can do it also.
Referencing http://ubuntuforums.org/showthread.php?t=308065
