Vuforia Image Target for mobile object

one possible option I see is to fix  the object to the eye vector of the device - so means you could first scan you target - this will initialize the coordinate system of you object and when it succeeded then fix the model e.g. to the eye vector on a current distance at the movement (so possibly you can fix it when the  tracking starts or with explicitly command - e.g. voice or click on obj) So this may have the effect that the 3d augmentation will move with you device .  In the post : https://community.ptc.com/t5/Vuforia-Studio-and-Chalk-Tech/How-can-we-make-a-3D-Widget-on-HoloLens-visible-in-front-of-me/ta-p/658541  you can see some techniques which explain how to move a 3d object depending on the eye vector on particular distance from the device position, but the movement described in the post is static - so there it will update the object  via explicit command and is not continuous  during the tracking but I think this could work als during the tracking  event callback 

$rootScope.$on('tracking', function( tracker,fargs ) {/***your code here ***/});