I used to work in a flower shop and we always used and gave little packets of cut flower solution with a purchase. the little packets do not last very long. the water needs changed way before the flowers are dead. One day I happened to have some flat soda in a bottle and used it for flower solution, since it wasn't fit to drink, and I figured since it had some sugar in it it probably would be okay for my flowers. I think it worked much better than the little packets of preservative. I'm not sure what kind it was other than it was a clear pop. I just happened to think of posting this here since I have had my delphiniums on the table now for about 5 days and they still look okay. This time I used fresh pop and diluted it with water. Try it and see if it works for you and let us all know.
I haven't used the asprin in the water. I can't imagine what the asprin would do for the flower. :-? Do you think the cut stem hurts?