But I'm really glad they didn't go with Tony being able to call the armor from his own bones...
Wow, that's weird
"The Undersheath to the Iron Man suit components was super-compressed and stored in the hollows of Stark’s bones. The sheath material exited through skeletal pores and slid between all cells to self-assemble a new “skin” around him. This skin provides a complete interface to the Iron Man suit components and can perform numerous other functions. (The process in reverse withdrew the Undersheath back into these specially modified areas of Tony Stark’s bone marrow tissue.)"
It does seem "out there", but I can see it working in live action like the quicksilver from The Invisible Man