If you want to do this, and I have not idea if its worth it or not, but what else are you going to do with the extra speakers. And sounds lie a fun weekend project! I say rig them up temporary style somehow and see if its worth a permanent install.
couple ideas for that if you are handy.
1) drop wires behind the drywall, if it is drywall. It is not super hard unless there is bracing in the way what would stop the wire...there often is. You should get wire rated for in wall installation. it is a bit messy. but not as messy as gutting a cow.
or
2) you could get some tape speaker wire. Such as this stuff:
https://www.amazon.com/dp/B005SUM1P...t=&hvlocphy=9027581&hvtargid=pla-311461664304
Apparently, not only will this stuff stick onto the wall, it is thin enough that you can also also spakel over it, like it was drywall tape, and then lightly sand and paint it to make it invisible.
The termination is a pain apparently unless you use their terminal block adapter things.
I have never used this and the geometry may create high levels of capacitance but I think its fine for relatively short runs and use like you are talking about.
There are other gauges and some other companies make similar stuff for a bit less.
3) REALLY nice looking wires...
