..Not familar with the Chevy Sonic, but it doesn't already have a hitch receiver on the back, does it? If so, all you have to do is buy a cheap drawbar and 2" ball, and you will then have an easy way to move the dolly around.
Thats what we did when we towed with a dolly. Dollies are light enough that most can be moved around by hand, but being able to move it with your towed vehicle will make it much easier. Especially if you have to move it a good ways. You may even want to look into installing a simple Class II hitch on your Sonic for this, if thats a realistic option.
More I'm thinking about it, I seem to recall that the dollies U-haul rents are some pretty stout (read: HEAVY) dollies. They may be a bit more difficult to move by hand. If towing the dolly around with your Sonic isn't an option, I'd try to get a pull-thru site like already said. Then, you probably won't ever have to move it.
I like the idea also, of just buying a dolly and selling it when you're done with it. Thats what we did, and we found there is a pretty good used market for those things.