For what it is worth, I am able to get my large road bike in the back seat of my 2000 Neon, if I take the front wheel off. I admit it is tight, and, like Stapfam says, I have to watch out for grease from the chain, gears, etc., getting on the bottom portion of the back seat, but it is doable.
I'm a bit curious as to why you don't or can't get your leg over a regular bike's seat? Is it a physical problem? Or, you just feel uncomfortable.
My wife (73 in November) rides a "mixte" hybrid - lower top tube - which she steps through instead o putting her leg over the seat, as I do.