It's a fun idea, Paul, and might yield some interesting examples, but I agree with Mysha, more suitable for a discussion thread than an actual performance, which would be unwieldy to say the least, even if the sequential and overlap issues of zoom could be overcome. It's indicative tho', that almost all of the examples that spring readily to mind involve traditional tunes - and several of them are already done as "song-tune combis" in performance. Midnight on the Water, steady and slow...
With "songs within songs" tho', a full combi rendition would be less satisfying simply because of the desired effect of the placing within the original creation, IMHO. Take the above-mentioned Waltzing Matilda, which has its own designated placing and Purpose.