trance should be a little scary. like obviously part of it is being disarming and lulling and thats all well and good but once you have the door open you might as well move your stuff inside. there should be, at all times, a quiet little "what's happening to me? what's happening to my brain??" thought you're working to quiet but never silence.
this is why your visuals should be a little frightful instead of seamless. plugging a computer into them? make the injection hurt a lil! you'll be there to comfort them after the sharp pain, right?
it's good for verisimilitude, too. for trust, even. when you tell them it's going to hurt, try to hide (hard as it may be) how much you're going to enjoy watching them squirm. no, your hands are tied. it had to hurt a little. but you'll be there to make it all better.
every speed bump on your way is a chance to reassert yourself as being on their side. when an instruction doesn't quite stick, or they remember something they weren't supposed to, it's not your fault and it's not their fault! the equipment's quite old. or alien. or arcane. that throbbing little trickling pain in the back of their neck is-- well, they don't have to worry about it. you'll patch them up, plug the connector back in (this might hurt, darling -- better hold my hand tighter), and then everything'll run a little smoother.
you're on their side. (right?) you're in control of the situation. (how much control?) everything's going to be okay. (according to... who?)
let the doubts build, and fester, and then tell them to plug the wire in a little tighter. tell them their eyes should meet yours, and they should hold your hand, and they should let all those doubts melt into you. you'll take care of it.
you'll take care of them. you'll soothe all their worries away.
(maybe you'll just keep a few. as a treat.)