We just bit the bullet too - we put a big thick towel under her butt to protect her carseat and hoped and prayed for the best LOL.
She actually hasn't had any accidents out yet - the first time she had to use the loo outside of home she freaked out a bit but once I coaxed her on there she's been fine about it since.
Childcare was fine, she's in FDC and her FDC carer was as keen as me for her to be trained so she was happy for her to go in undies, I just send a couple of pairs and a change of clothes.
If he's really not ready for the "leap" and has a few accidents you go back to nappies for outings...we did this a few times and it didn't seem to affect her progress (which was slow no matter what we did!)