Have you got head rests ?, if so get a clear bit of perspex from B & Q and some elastic, cut a sheet of perspex that fills the gap between the headrests and secure it to the headrests with the elastic, should cost you about £15 + an hour of your time
and
Having had one on my last Aero, I have to say that it is quite effective. It doesn't stop the wind completely. What it does is stop it battering the back of your head. It's abit like different types of screens on bike fairings change the wind dynamics greatly even though it may only be a subtle difference between one screen and another.
The problem of course is they do not look very attractive. I may have a go with the perspex but I don't think I'd get a standard one again (assuming of course someone made one as my old one would not fit a series 4).
Our friend Eddie was talking about a windstop on a +4, on a trad'.
On an Aero, with a larger windscreen and a different shape, the global aerodynamic is quite different, as its effects on the passengers.
For phylosophical reasons I don't want to visualize the aspect of a perspex sheat attached with rubbers on a trad' and I keep recommending a scarf and a nice knitted hood.
You will look maybe ridiculous (it strongly depends of the knitting style of the said hood), but the car will remain aestheticaly intact.
H3