I've sketched up a box to go over the hepa filter intake so air is drawn from an area away from the AC out vent. Drawings and wireframe render of the assembly are attached below. Cheapish acrylic should be fine. Not sure if I should make the intake further away but I don't want to constrict the inflow too much.
The intake is 3" above main body of unit with total of 6.3" to the AC outlet. The idea of the box is to pull air from the side where it will be closer to average (well mixed) room temperature.
Please comment on anything stupid that should be changed.