So in the two live action films, it's shown that the Guyver armor is stored in the body. You see the tendrils come through the receivers on Sean's neck several times. I've always noticed this, but wondered why. Does anyone know, or at least suspect why? Was it simply an artistic liberty, or perhaps done for budgetary reasons? Since I'm sure trying the flashy transformation sequence from the anime would be too costly. 

when they made the miniatures for the transformation sequence, they needed some way to hold the armour pieces in mid air, it would have been very difficult without some structure, so I guess they used those tendrils and it developed from there.

It can be assumed the tendrils at least are stored in the host body - most iteration of the bonding process describes it as being a painful experience as the tendrils pierce and invade the host body in order to boost it to its ultimate potential. The receivers are a physical manifestation of a bio-boosted human and at least grants low level telepathy/communication between guyvers. It's mainly the armor itself along with the control medal and powered orbs that would be stored in hyperspace awaiting its next activation.

However,  I don't recall it being shown (except movies) upon activation the tendrils coming out from the receivers - I think this is just artistic freedom of the directors. I'd imagine the tendrils would come out instantly to wrap around host and attached to the armor in a fashion similar to a klyntar symbiote on its host.