I've done it a couple of times now. You have to call in, they usually waive the booking fee 1. because it takes forever and 2. it's not possible to do online by yourself. Make sure when you call in you tell them you want Disneyworld in Florida tickets, have them repeat back to you exactly the ticket you want and have the price on hand from the website. They will put you on hold, call into Disney, arrange for the tickets and come back and tell you the price and it should match exactly. Disney will charge through to your credit card and then BMO will refund the equivalent points if you have enough or just whatever you have available and the rest will just stay on your card. Have them give you your Disney Confirmation number before you get off the phone and you should be able to link it right away. I had a little trouble linking mine but I just called in to the Annual Passholder help line and they had me fixed up within 5 minutes, some kind of cyberspace ticket issue she didn't think was related to the fact I had purchased them with points through BMO. Good to know as well I have been able to book Halloween and Christmas Party tickets this way before and I'm about to find out if I can book tours with them as well because I'm going to be booking the Wild Africa Trek for my second trip next year in November.
I used the point for flights for the first time last month when I went, I booked Southwest from Buffalo to Orlando. I was originally worried that I wouldn't have control over the ticket i.e. to make changes etc, but once I had done it they sent me a copy of the exact same confirmation I would have received if I booked them myself.