My suggestion was to see about either Zeke's idea or register for two ahead of time. If you register for Lakefront early enough, it's not that expensive. For Lakefront, I'd also highly doubt you'd have to book a hotel room ahead of time. I think the Milwaukee metro has more than enough hotel rooms to support a marathon with 2000 participants.
Unfortunately, while you used to be able to register on the morning of the race for Lakefront, you no longer can. Registration filled up I believe about a month in advance last year.
I understand that this can be expensive, which is the reason I didn't do it twice when I signed up for Lakefront. After being burned both times, I've found myself reconsidering whether, when signing up for a race that could be so significantly affected by the weather, the investment of having a back up plan is worthwhile.