Use a bottle jack, but you might need two.  One shorter (say a 4 ton) to make sure you can get under the axle, and a 2nd stronger (12 ton) that is usually taller.  At least that is what I had to use to change my sisters tires this last year.
Just make sure that you check whatever you get to make sure it works before you need it.
And in regard to those that are proponents of roadside assistance, I would be cautious.  Great service if you are in town.  But there are times when it takes forever for them to get to you.  My sister had 3 tread separations last year (which can be a whole other subject).  Twice she called roadside assistance, and had to wait over 3 hours each time.  I am not sure why you would be willing to wait that long when changing a flat should be a 15 minute ordeal. 
Even if you are not physically able to do it yourself, if you have the equipment, a good samaritan will possibly help you out if you have the equipment to change it.