I LOVE Arby's RB w Au Jouis sauce! Sooooo, instead of giving in and going there I put a roast in the crock pot.
-SB approved roast
-1 packet Liption Onion Soup Mix
-Chopped Celery
-Chopped Garlic
-Water
I let it cook all day and it tastes just like Au Jouis sauce!!! Soooo good!
Just thought I'd share!

I bet some others will have some better suggestions for future use.
I'd replace the sugar w/ Splenda just to be safe, though.