Hey ajhoff83 welcome to the forums, there are a number of guys that have bobbed the LS650. Just do a search and check out what other people have done. I've seen quite a few side mount plate holders in various posts. I'm not sure if anyone has directly mounted them with the axle bolt or not, but 1/4" seems a bit thick. Here's a pic of SimonTuffGuy's bike with a side mount I came across quick doing a seach, it's hard to see if it's mounted using the axle bolt or not though.
Also make sure your state laws don't require the plate to be mounted horizontally before you dive in