A lot of caregivers have a minimum three days a week for this reason - it gives them a couple good days and the more good days they have the sooner they accept the first day.
Another alternate and I discuss this with families asking for part time - they don't like it but too bad. I rarely take part time now but when I do it is done with the idea that if the child settles into routine fine after a couple weeks then ok. If not I require the child to come full time till they are settled - they need to become more familiar with the new routines and what is expected, get used to not being with mom etc. Once settled in we start gradually cutting back the days till child is down to 2-3 days as needed. If that never happens then usually family leaves because they can't afford to pay for full time. But at least you get peace if they leave.
The fact the child settles on Wed means it should go quickly so probably 2-3 weeks of full time is all you would need or even 4 days a week for a month, then 3 then 2 - ideally mom will get where she loves that one day off no work no child to get things done and leaves him in care 3 days.