Just to add to the debate/discussion - I use an Exodus two bike carrier that fits onto the towbar (£60 from Halfords). I do, however, restrict its use to just carrying the one electric bike. Yes, the length of the bike is longer than the width of the car - but its not longer than the width of the car when the wing mirrors are taken into account. Works for me - very convenient and at a very reasonable cost.
http://www.halfords.com/cycling/bike-racks/towbar-mounted-bike-racks/exodus-2-bike-towbar-mounted-cycle-carrier#
http://www.halfords.com/cycling/bike-racks/towbar-mounted-bike-racks/exodus-2-bike-towbar-mounted-cycle-carrier#