If he buys new shares with T+1 settlement he can deliver those instead. The IRS would also allow buying with T+2 settlement and shorting against the box for a day, but most brokers don't support that.
That's my understanding, and it's what IB describes in the link in my first post. The wording in the tax law about holding periods always references delivery date, not trade date.
Interesting - thanks for the additional info and my apologies for not chiming back in until just now - I missed the email notification of new comments on this thread. Regarding Robert Morse's suggestion to exit or roll the option - I need to look into and learn more about rolling options. Again I'm just learning about trading options through reading and trial and error. I did end up exiting the option because the stock price was hovering around the strike price on Friday afternoon and I didn't want to get assigned. However, by the end of the day the option expired worthless and I would've been better off just letting it ride. To elt894's point about placing a T+1 order after receiving the assignment notification - the example given is for early assignment. Is it also possible to do this after expiration? So if the option expires on Friday after close and I am assigned, can I purchase T+1 shares on Monday morning?
I'm not looking back to regret my decision but just as an opportunity to learn more. And I sincerely appreciate the sentiment and advice and the knowledge being shared.