You can't do that without nuking most of your installation, as itActually, I was able to do it on current cooker, but not my "stable" cooker from May 18. On current cooker, you can force it on, and libstdc++5 doesn't get uninstalled. On the older cooker it did (and everything broke). Reinstalling libstdc++5 again left libstdc++2 in place, fixed the problems, and left a working Flash plugin.
uninstalls the other version of libstdc++, which tons of packages depend
on.
Someday I may actually understand this stuff.