TowPac www.towpacusa.com makes a pretty stout kit. they keep the rear wheel for traction but add a couple extra wheels. Their kit can be installed/removed in about 20 minutes tops. If it interests you, try and find one on Craigslist. The mounting kits are bike specific and can be ordered separately from the manufacturer for a couple hundred dollars.

I put one on my Honda PS250 for the wife. She started having some troubles, but wanted to keep riding.