Thanks for the quick reply - and the additional info about where the weight is applied. I figure if the 250 lbs is applied 2 feet from the receiver, I'm about at the limit - assuming the 500# is correct. In the long past, we used to pull the handlebars off the bikes to get them to fit. Without the bars sticking out, I am sure that the supporting rail could be 12" from the receiver.
Another option is to go with a little Honda CT70. Handlebars and footpegs fold up, and it could literally fit within the trunk... I think. Not quite as useful as a little dual sport though...
Would you have any info to confirm the max tongue weight?