As you can see from the butterfly species list, there are quite a few butterflies that don't feed on flower nectar or sap. Some feed on carrion and others feed on mud, probably dining on the waterway version of roadkill. The former is best left to Mother Nature. Other lures include places for basking and, for those that do sip nectar, nectar feeders.
 
Fruit
Fermenting fruit is something you can make at home without attracting too much attention from the neighbors (it depends on just how nosy they are and probably how much fruit you put out as a lure). If you have fruit trees, try not picking the fruit up and see what happens. If you attract "vermin" rather than butterflies, nix that idea.
 
You can make a fruit mixture and spread it on fence posts, rocks, tree trunks, whatever is handy. This is called "sugaring" and will attract nectar feeders as well. Basically, mix up some mashed fruit with a sugar source (sugar, molasses, corn syrup, honey) and let it sit for a few hours, then put it out for the butterflies.
 
In Peter D. Stiling's Florida Butterflies and Other Insects, he includes a basic recipe:
 
He also notes that some people soak sponges in a sugar solution and hang them from trees at dusk to attract butterflies and moths.
 
Experiment with the basic idea and see what happens. What were you going to do with that rotten banana anyway?
 
Basking
Butterflies bask in the sun to raise their body temperatures so they can fly. You can accomodate them by including some flat rocks in your garden.
 
If you have an area that gradually slopes to the south, it's an ideal spot for a butterfly rock garden. Include flat stones and low-growing butterfly plants, such as lantana, Stoke's aster, and clover.
 
Puddling
Some butterflies sip moisture and nutrients from moist soil. You can provide a puddle by allowing water to stand in a depression in your yard or by placing sand in a wide shallow container and keeping it moist. Puddles should be in an open area.
 
Nectar feeders
Butterfly feeders, which hold nectar (and sometimes pieces of fruit), can be purchased. You can also make your own. One method is to place a sponge, plastic pot scrubber, or other absorbent material in a saucer of nectar. The saucer should be placed amongst nectar plants, a few inches higher than the blooms. Another method, which I've tried without success, is to hang a small nectar-filled jar, such as a baby food jar, upside down among the nectar plants. Poke a small hole in the lid and plug it with a cotton ball. A red lid or small strips of red cloth will help attract butterflies.
 
Nectar is made by combining 4 parts water with 1 part white granulated sugar. Boil the solution until the sugar is dissolved and allow it to cool. Store extra solution in the refrigerator for up to a week.
 
Wash feeders thoroughly once or twice a week (more often in warmer weather) to prevent mold from forming.
 
If ants are attracted to your feeder, try coating their access route with petroleum jelly or mineral oil.