oh, yeah. I'm not sure how noticeable it would be, but you're right. [try it and see if you can notice the difference... worth a shot...]
For something that directly copies, the only thing I've used is vdub. I suppose you could make two videos that have the same length as the songs, add those songs with vdub, then append the two together, and demux the audio.
It sounds ridiculous, but I did it just now [for fun

] and it worked; I ended up with one 19,557KB file from two that were 9,364KB and 10,193KB
there's probably an easier way though...