You'd have to contact AAMC and ask for it, because the zoom feature is for people with disabilities according to them. I think it said that on e-mcat also.
I had a hard time focusing because of the font when I practiced also. The font on my laptop was too small, because my laptop has a 13.3" screen with 1600x900 resolution. I switched to a desktop with a 19" screen and a 1680x1050 resolution but the font was too big now.
2 days ago when I took the real thing the font didn't bother me at all. Trust me you'll be way too busy trying to answer questions to notice. The screen at the testing center was ~ 14-15" with a horrible resolution, the font was too big, but it wasn't an issue.