I think he should wear the tan uniform to the meeting out of the visibility of that uniform being the "public" uniform, and have an Eagle patch of some sort. I would do the knot with the medal, and just leave the knot on till the ceremony.
For the Venturing uniform, I would actually skip the badge... At least in my experience, I wore knots out of respect because the youth females (well all females) can't earn a RANK badge of any kind and wear it on that pocket. If you want green knots, visit - http://www.sageventure.com/store/knots.html for proper matching green themed knots.
If you become a Life Member of the National Eagle Scout Association, remember to get the new knot with the Silver Border, and wear the blue rope tips of the knot pointing towards the OA flap pocket (either NESA or regular version).
"The new square knot may be purchased by NESA Life Members who show their NESA Life Member card at their local Scout shop. If they dont have them in stock, they can order one for you. The item number is 18092. You may buy one for each uniform you have."
Just my thoughts, I was in a similar predicament when I was the OA lodge chief and I wore the knot with medal in a tan uniform. Get it pressed for the big day!