Did some digging and found out the Aspire SE model came with a rear hatch spoiler. My estimation puts the height just underneath the template, which should be good enough for attached flow.
I'm thinking of using it as a mount for a kammback if I can find one for cheap. The Wings West ones cost nearly $200.
Or, I might try vortex generators and see if that helps. The shape of the Aspire's rear end is very similar to the shape of the body used in this video:
Without VGs:
The Aspire's hatch is a 25* average with a maximum angle of 35*, with the glass starting at about 22*. I'll be doing some tuft testing to find the separation point when the weather clears up.
Also, I took it out on the highway for the first time this morning. 5th gear runs the engine at 2400 RPM at 55 MPH. Not too bad, but taller tires might help some.