You could always rent a vehicle for your remaining driving needs. For 10% of total driving that might be somewhat impractical, but 10% sounds like a pretty high estimate for trips that would challenge the Model S's range. That's one long-range trip every week and a half. Yes, there are people who drive like that, but they are very much in the minority.

If you drive to grandma's/the in-laws/"up to the cabin" three or four times a year, that's only 1% of trips (assuming you commute every day and run local errands on the weekends). Most families in the US already have multiple vehicles. Why can't one be an electric?