For this:
"We still have prepaid expenses and accrued expenses that need to be adjusted manually to get a true cash financial statement."
You don't Make the adjustment in QB; you take the values into consideration for tax reporting.
"Accrued" expense would be AP bills. That already doesn't show on cash basis reporting.
If you want your client Not to have prepaid expense, then they need to Stop Posting it as an other asset. Tell them to use Expense directly.
Whatever you decide, avoid using JE for this. That would be a mistake, in QB.