My seats don't fold down either on my 2001 Mitsubuishi Galant, which is just stupid. When I first started riding, I used my Saris rack to get to rides, but I never really liked using it and I didn't like leaving the bike on the rack unattended and exposed to the elements, which made going to rides straight from work difficult. I figured out that I could slip the bike in behind the front seats. I have to take the front wheel off and turn the fork sideways, but it otherwise fits.

It's a 50 cm road bike; it it were any bigger I doubt it would work. I use a velcro strap to hold the bike in place behind the driver's seat. Granted, it has scuffed up the back a bit from the crank and chain, but given that I plan to keep the car indefinitely, I don't worry about it all that much.

Unfortunately, I'm now parking in a new parking garage (my old garage was a secure government lot that's now under construction). I don't feel comfortable leaving my bike in the car where you can see it so my riding habits after work have changed somewhat. I can get it in the trunk if I take both wheels off, but that's kind of a PITA.