I never quite understood how that could be accomplished. I guess snap the bird in and let it feed. But what if there is weather suddenly approaching or something or someone else? A stray dog?
What I do is let them break into the kill, maybe give them time to eat the lungs, heart and liver of whatever it is, then present them with something else that I brought along, on the glove...sort of slip into their face, they will grip it with beak or step on, then lift up both the hawk and the kill, but slip the kill away while they are eating the food you brought along (your controlled amount). Either that or many people put the garnished lure down next to them and hope they will transfer over to it, many do without a hassle because they've been doing it that way since about this age your bird is now.
But, if you look at youtube videos of various small accipiters being flown (Sharp-shinned Hawks, Eurasian Spars, Crested Goshawks, Cooper's Hawks, etc.) you will see that just about everyone feeds on the fist at some point in the process. You might get away with it for quite some time, barring any interruptions or obstacles. But eventually you'll be forced to pick them up and perhaps very unceremoniously due to the circumstances. And if the bird isn't familiar with the process of being picked up from the kill or with the kill, you may scare them badly and ruin the experience with them. Trust is sort of an important thing with imprints of any kind, so you must, ideally, try to preserve it as often as possible from any threats.