What kind of top does your trailer have? could a bike rack, the type that straps on a trunk or hatch be mounted on the back? The leverage action of a receiver bike rack, especially on the back of a trailer, can be pretty dramatic.
Just be sure that what ever you add to the back of the trailer doesn't reduce your tongue weight too much. Tongue weight should be 12-15% of total trailer weight. If you have less than that, the trailer can start to sway. On the back of a 'motor bike' I'd be afraid the trailer might outweigh the tow vehicle. Also, If you don't have brakes on the trailer you've only got two motorcycle tires doing all the stopping.