If you wanna go the cheap route...just pee in it. (OK, maybe you shouldn't do that)
I just put water wetter in my bike. Still had 50/50 in it, and water wetter claims to make the bike run cooler, even with 50/50. I need to change the coolant, but have been lazy....have too much fun riding when it is nice and not enough clean room in the garage to wrench when it is not nice. Guess I need to clean the garage soon.
2004 Triumph Speed Triple SE (Speedy - Street Bike)
2002 Suzuki GSX-R600 (Shamu - Track Bike)