It's not possible. Every state that uses the Multistate exam administers the exam on the same day, with their state specific day either before or after the multistate. NY I think usually has their state specific day first, and the multistate second. The CA bar exam is different in that it is 3 days long, with the Multistate in the middle. So without being able to sit two exams simultaneously 3000 miles apart, it's impossible to take them both during the same administration.
I suggest that you do it this way: you take CA first. Why? Well, NY grants MBE reciprocity, whereas CA does not. I learned this the hard way. So if you're deadset on taking both in a July-Feb type arrangement, you have two options: 1) you take a full 2 NY bar exam in July, and follow up with a full 3 day CA bar exam in Feb as CA does not grant reciprocity, or 2) you take the full 3 day CA bar exam in July, and take a 1 day NY bar exam in Feb.A couple of notes:-I'm fairly certain that taking the MBE twice has taken at least 1 year off my life-if you're starting out in NY biglaw (as i was ), make sure to double check with your firm before you sign up for CA first. unfortunately for me, i was req'd to take NY first (i.e. it wasn't optional if i wanted to keep my job).-studying for the CA bar on my own while attempting to keep up with work assignments and billables was a f'ing nightmare. honestly, i don't recommend the process. more specifically, only do this to yourself if you **ABSOLUTELY KNOW** that at some point in the relatively near future you want to use your CA bar membership for practice. don't sign up for this thing because "oh what the hell i studied pretty hard in July and i think that i remember a lot of it and it would probably look pretty good to have CA and NY on the resume" - nope, not worth it.