Heat transfer ... heat will transfer or be driven toward a "cooler" medium via three methods... conduction, convection, and radiation.
Right now, direct sun heating, radiation heating, is conducted via the metal roll-up doors, and are both convected and conducted to the inside of your garage.
Sort of changing out your roll-up doors with panel-insulated ones, I would build "temporary" outside insulated panel walls that are clad to protect the insulation and framing materials.
1/4 plywood for the exterior side with 1 x 2 frames infilled with rigid insulation. To make it more manageable, build these panels vertically at 10 feet but with hinges or something to keep the separate panels together. Adding a perimeter gasket to the panels will stop convection heat transfer.
The insulated panels and the in-filled air gap it makes with the roll-up doors will mitigate the heat transfer tremendously.
Of course, the above would be a PITA if you need to constantly use your roll-up doors.