Withdrawals from retirement accounts can count as income for mortgage purposes as long as they are documented and likely to continue. Or so I've heard.

Yes. We have done this 5 times on refi's in retirement. The rules are in the FNMA guidelines. Most mortgage processors are unaware of this, as it is not very common.
Basically, they want it to look as if it was a regular paycheck.

(I used to know the section of the FNMA guideline, but it has been so long I don't remember it anymore. Google & download it. You just need to point them to the section. It is not likely that I'll be refinancing my 2.5% mortgage.)

1) Show that you have directed the retirement account (IRA/401K) custodian to withdraw $XXX a month and send it to you. This can be done by showing them the form you filled out at the broker. Or other means.
The $XXX needs to be large enough to satisfy the 28/36 rule.

One time they wanted to see the check. So I send them a scan of the check. But I did not cash the check. After the loan closed, I called the broker to re-deposit the check under the 60 day rule, and he said he could just cancel the check as if I never took the withdrawal.
One time they wanted to see the deposit hit my checking account. So I did an ACH from a taxable account at the same broker as the IRA, for the same amount.
One time they just wanted me to state that I did monthly withdrawals.

2) The account has enough money to cover 36 months of the withdrawals.

After the loan closes, you can cease the automatic withdrawals.