Just tried this today as we need to haul our bikes a bit further for some rides... Wow! It's actually easier than I thought... put two bikes in there take less than 3 min on the second try... I'm sure it'll be even quicker next time.
Yes, it's entirely do-able. You can fit two road bikes in there without even adjusting the seat.
The bikes I'm using are 50cm and 52cm in sizes, if you have a taller bike, you may need to adjust seatpost a bit to have them fit in the trunk and/or rear passenger seats.
Use plenty covers to protect seats from getting grease on them.
Make sure rear derailleur from bike in the trunk is not touching the bike in the rear passenger seat... Use padding if necessary.
Saved me $800+ on bike rack options for Honda Clarity, I was really shocked to find the hassle of installing a hitch on this thing.
Downside? No rear passenger space, no trunk space... And you might scratch/damage the interior of the car from handling the bicycles.