This is completely theoretical, and probably even more ludicrous as I
think of it being plausible cross-browser...
But in theory if you did something like this
var A = function(){ alert("First definition");}
A();
var A = function(){ alert("Second definition"); };
A();
Would behave as such, so that you could load jquery and all dependent
scripts first, then load prototype and all of its dependent scripts
subsequent to that and get away with it? Give it a shot and let us
know...