Any of the above suggestions will work just fine - 20% honey/water is correct and Juicy Juice may be used "full strength". Fresh cut flowers (or those in pots) also work very well. Fresh fruit and honey/water solutions should be changed daily to keep things fresh and prevent fermentation. Alternatively, Monarch Watch has an Artificial Nectar Kit available:
This kit includes 1 clear plastic feeding dish, 1 feeding scrubber, and nectar mix (ingredients you wouldn't normally find in your kitchen). Makes 1 liter of nectar and will not ferment.
Hope this helps!