I've made one [crankshaft seal installer] before for another car.
I cut a thick block of wood just a little bigger than the seal. I then drilled a hole in the middle of it the size of the crankshaft diameter. Then I used washers with outer diameters bigger than the hole size I used, and inner diameters that accommodated the damper pulley bolt. I used that bolt to tighten it down to press the seal in evenly.
That was more work than using the right tool (which I didn't have), but "when all you have is a hammer, everything starts to look like a nail."