You may be a candidate to build one of Mike Sandlin's "Airchairs".

They're soarable, Floyd Fronius has flown one about 60 miles or so.
They're car toppable.
They're a pretty quick build.
If you want "slightly better than primary glider performance", you might
consider putting a fairing on a GOAT, and reinventing the secondary glider.

Mike's documentation of what he has done (he does not call them plans) are
very complete, and available for free on his website.

Take a look at http://home.att.net/~m--sandlin/bug.htm and see if that meets
your criteria.

If you don't already fly, you'll still need instruction in something with
three-axis controls.

Tim Ward