Not aware of any grad school programs that allow substitution of the MCAT for the GRE, but you could always ask at programs you're interested in applying to.
How did you do on your SAT? If you're a generally good test-taker, you can just take the GRE cold. That's what I did. I got about the same score on both of those tests after taking them both cold. (We didn't do the whole test prep thing in the late 80s/early 90s when I was in high school.) If you have to take a subject test, that might be tougher to do cold if you haven't seen the material in a while. But if you're fresh out of college and you majored in the same subject, it probably won't be a huge obstacle for you to achieve a decent score even on a subject test. I didn't study for the chemistry subject test, but I scored highly enough on the ACS UG exam and the general GRE that they didn't even make me take it.
If you're not a naturally good test-taker, then studying and practice is not optional. If you can't squeeze any studying in over the next 1-2 months, you should postpone your app until next semester so that you have time to prepare properly. One good thing about grad school is that, unlike med school, it's entirely possible to start in January instead of in August at many institutions. So you don't necessarily have to sit out for an entire year if you can't be ready to start in August. You can just apply to start the following semester instead.