I have a CX7 with the same transfer case and diff. I have never had a problem with a pair of tyres (on one axle) being more worn than the other pair. Tyre wear is usually limited to about 5mm between new and illegal.
If your rears are in good condition I would try leaving them on and start with two new front tyres. The fronts will wear quicker than the rear until they are all similar.
If you buy the same tyre size front and rear it should be OK. If it is causing problems you can buy the other pair of tyres easily to correct the problem.
CX7 - The younger, taller and sexier replacement for the MPS6 and the first car designed around the MZR DISI
2007 CX7 2.3 DISI AWD Ice Blue | HID's | ETS TMIC | Cobb XLE BOV | CX9 20" wheels | 245/50/20 Scorpion STR's | CS HPFP | CX9 Brakes | Pedders Sports Ryders -40mm | CS Turbo | JBR 3.5" WPI | Cooling Mist WMI |Versatune