jackthedog,
I feel your frustration. I wish I had the answer for you. Luckily your son is older and will hopefully know if it is unsafe to get in the vehicle. I also felt I had no choice and had to let XAH drive with my then 3 year old son. Fast forward 3 years and I had to pick my sons up (luckily my 15 year old decided to go that weekend-he usually didn't) on a Sunday morning because my XAH was going to drive with them and he could barely stand!
I think the idea of texting "x" is really smart. It sucks to put him in that situation but the bottom line is his safety is what is important. I admit I do/will end up doing all the driving for my children for a very long time now. Knowing that relapse can happen at ANY point my XAH will not have the children for long periods and will be supervised for a long period. It's not ideal and gives me very limited free time or flexibility but I have peace of mind that my children are safe.
Will he agree to no alcohol within 12 hours of visit?