Why do you need to have it sit upright? Lay the bike down and your options open up immensely.

I have XL size bikes with the saddle raised quite high and I have to lean them over to get them into the back of my Grand Caravan.

ALso, why not ask your co-worker if you can try to put your mtb in his Honda, just for 'fit' purposes?

And regarding the Honda Fit, those are nice cars! I was considering getting one, but the price of gas has fallen and that means my Dodge can stay on the road for a bit longer. I rented a Nisan Versa a couple years ago, and while it was decent to drive, it was completely underpowered when it had to carry more than one adult.