As I'm sure you're aware, there really is no way around actually doing the technique, if you want to master it. Why not simply break koshinage into small sections of movement that you perform until a suitable level of comfort is obtained? When you feel comfortable enough with one section, then add another section and so on until the technique can be performed entirely without breaks. I get my students to do this with koshinage quite often. They practice the moment of connection to uke, then the moving of their hips into and below uke's, then the loading of uke across the lower back/hips, and finally the dropping of uke to the floor. Works well for them; perhaps it would be useful for you to do it this way, too. Given your touch aversion, you'll probably want to use as uke the person in your dojo with whom you have the most comfort already. Just my two cents.