I'm not sure why this didn't occur to us earlier, but another option would be to change the makefile to compile with g++-4.1, not "g++" which might default to g++-4.2. The problem is that not all systems might use the same nomenclature and you might end up with code that reports a missing compiler.
That's at best a temporary fix for a limited audience. Many people won't keep older versions of their compiler around, especially if the upgrade was the result of an automated apt-get yast, or whatever package manager your particular system uses.
If GNU feels gcc 4.2 is stable enough to release it, I would assume they plan to depreciate the 4.1 compiler. I would also expect new OS installations to start migrating to the new compiler as the default. It might take a year, but then we'll be right back at the same place again.
NOTE: I am assuming here that fixing a 4.2 warning does not cause 4.1 to generate a different warning. It wouldn't make sense for it to be that way, but if it does... then it might be a valid argument to try and delay changes until 4.1 is further out of circulation.
My own debian system is using 4.1.2, and debian is notoriously slow at accepting new versions into their non-bleeding-edge distros.