It's surprisingly easy!
This isn't the first time Electronic Arts-published games have seen crossover items, and it will almost certainly not be the last. Those who have played Mass Effect 3 and still have the save file to prove it need only buy a copy of Dead Space 3 on the same platform to access the prior series' iconic N7 armor. Yep, that's it. Catch the embedded video to see it in action.
According to EA, this will work on PC, PlayStation 3, and Xbox 360. Having not seen what else there is, it's too early to tell if this will be the armor I stick with in Dead Space 3, but it seems like a strong contender from an aesthetic standpoint.