That's exactly where my head went too, initially. But genuine pharmaceutical-grade diluent is so easy to find and costs barely over a dollar per reconstituted vial, hate the idea of ruining a mixed vial just to save that dollar.
Even considered brewing my own preservative solution at home, since I already make a few basic solvents a couple times yearly for other projects. Kind of leans into that whole amateur-chemist vibe. (Turns out synthesizing peptides themselves would actually be simpler than making that particular solvent.)