Odie is a week or so younger than Harvey - he really has been a test at times...we still have at times, poo in his pen when I get home (I work 4 hours a day outside and work from home the rest of the time.
I know you feel it'll be cruel - but, maybe, just try it once for a very limited time - if he's in there with a divider at night, it won't be much different for him for the 30 minute school run (just maybe try it for that particular run at the mo) as long as he has space to turn round, stand and lay down, and drink his water...you won't need to do it for ever - just as part of this particular training process.
I don't know if this'll help - but about half an hour before I leave the house I turn the radio on, I get the BEST treats (for Harvey it's hotdogs!) and I spend a good 20 mins with him playing and training - then, just before I leave, he goes out for a wee and poo (even if he doesn't need one) I say "do wee's (or poos) and give him a minute or so to think about it...then it's in his crate/pen, no fuss, with kong (stuffed with kibble and peanut butter), radio still on, and out, without a word (I try and make sure he's really stuck in to his kong before I go)
Re: DAP diffuser - I really can't testify whether it was a huge help or not - but I think it did calm Harvey from the manic SA symptoms down to just being clingy - then we worked on the clinginess...it's worth a try - try online for one, it might be cheaper than a pet shop.
I know this is hard - I have one large advantage for being in a routine with Harvey as I don't have children, and it must be really hard juggling it all.
The best advice I was given was to not react when coming in if a poo is there (sometimes it's really hard to not shout "for goodness sake" (or similar with lots of swear words!!) but I come in, ignore the smell!!!!
open his pen, let him out - no words - as soon as he's done wee or poo outside, he gets all the cuddles he wants. Try to be calm (even if you're feeling really frustrated) - as they really do pick up on mood, and of course, he has no idea why he's picking up frustrated vibes off of you, as opposed to manic cheery ones he's feeling when he sees you...it then becomes a bit of a vicious circle - he'll be nervous...he'll poo, he'll be even more nervous...you'll be frustrated, etc etc etc - try to be really strict with yourself and consistent - even when you want to screeam!
I promise you, he has got better - small steps yes, but he has got better...in a week, inc weekends, I'll have one or two poos now. (before it was poos wee's distruction of pen, etc all the time)
Most of all (and if you've got this far without falling asleep, I applaud you!!) big
to you