Hmmm..Im kinda in the same boat you are and Im gonna go the additive route. I got the Urineluck additive that is just 2 little vials to add to the sample. The reason Im doing it this way is I worry about temperature with synthetic or someone elses speciman. They test for that right away and you better have it within range if you go that route.
Also, they are not permitted as far as I know to actually enter the bathroom with you.
Good luck..