Cheap, easy, and small is just a short 1/4" spacer or so that goes on like a big washer. However that's about as much as you can get out of them.
A bit more expensive would be to get some of Energy Suspension's stepped bump stops and run those. I have some on my Ranger, cost about $40 or so. You'd just need to find a bolt with the same thread as the threaded shaft of the OEM bumpstop. If you needed some more length just space them down some with stacks of large washers or something similar and use a longer bolt.
