Baja Bound will sometimes just rent their bikes out - you don't necessarily have to be part of a tour. They have had some bad experiences with people just renting however, so I'm not sure they haven't changed their policies. But its probably worth checking with Jennifer at Baja Bound to see.
2006 R1200GS; 2009 Husaberg Rally 570; 2011 Husaberg FE570
"Speak to me of summer, long winters longer than time can remember;
Setting up of other roads, travel on in old accustomed ways."